I currently have a Studio Mate.... It needs a bit of help reverb does not work and has not bias adjust.
Also looking at a YSR-1 ... Any pointers on this would be appreciated ..
I have a Marshall Silver Jubilee...Sovtek Mig 100H I converted to EL-34's and I now love ,another Mig 100H debating whether to change it, A mig 60, a four tube 6l6 Silvertone 1453 ??? (like to sell) a Marshall 9001/9005. H&K Cream Machine & Bluesmaster... A little 6v6 amp on the bread board (A specially Designed System) It has a 2 12ax7 front end with Cathode follower and a Itty bitty Amp based on the cream machine sort of a circuit which I hpoe to add an EZ-80 if ned's shipment gets here.
I buy and sell Industrial Equipment here in the Boston Area for the past 20 yrs or so... Thats It Whewwwwwwww!!!!!!!!!!1I also forgot to add I am new at building and Need reference Material if any body has got any thing Xtra let me Know ???
Can anybody tell me anything about the Traynor Studio Mate? It sounds like a 2x6BQ5 chassis like the Guitar Mate, but it is supposed to have 4 7" speakers and reverb/tremolo controls. ???
Mike MacLeod
I heard one at the Larrivee xmas party and it had an extremely nice sound ... I checked the amp out later on and was surprised to see two 6bq5's and 4 small speakers in a compact close back arrangement ... real coOoL
jc
I have not played around with mine much... I was wondering how well the reverb would work if I fixed it...I could not believe that it was capacitor coupled...Thought a transformer might be better... I also have not put in log pots which would help. I really liked the sound with a distortion pedal.
I am supposedly getting a YSR-1 anybody got experience with these ???
Bill
(... they're nice, the reverb is very clear - some cap coupled and still sounding fine ...)
>Can anybody tell me anything about the Traynor Studio Mate? It sounds like a 2x6BQ5 chassis like the Guitar Mate, but it is supposed to have 4 7" speakers and reverb/tremolo controls. ???
It is just a GuitarMate with 4x8" speakers. They often had the GM schematic inside with no name changes except on the faceplate-- the back panel even says YGM-4.
Kevin O'Connor
Aaron,
I own a Traynor TS-50B. Any info available on it? I need to repair it. I put my girlfriend's keyboard into it and blew it. Evidently, the amplitude of the keyboard's output is too high. Any ideas? Also, add me to the mailing list.
Thanks,
Larry Nagode
I got tired of all the people with Custom Specials kicking sand in my face. I finally bought one of my own. I have been looking for a YBA-3 for months. After years of turning down YBA-3s at Used Sound (Ottawa) because they wanted an outrageous $175 CDN, I have reconciled myself to the sad fact that YBA-3s are no longer available for that price. On phoning around last Thursday, I discovered that the Toronto branch of Song Bird Music had two Custom Specials, each for $395 CDN (about $280 US). One had no master volume, and Czech (Tesla) EL34 tubes (if I remember correctly), the other had a master volume and old North American 6CA7s. I bought the latter, feeling that the master volume amp would be a somewhat more recent version - though perhaps less collectable. The amp arrived today. It is in excellent condition and sounds great (noisy fan though). So far I have only heard it through a Celestion 18 mounted in what was a Traynor 4 X 12" cabinet.
I recently bought a Traynor 6X10" cabinet (without drivers) in anticipation of the YBA-3. It is annoying that the head is about two inches wider than the speaker cabinet. I gave away the 4X10" Traynor Cabinet and will put the four speakers removed from that into the 6X10" - and of course buy two additional Eminence 10020 (Martin Sound #1950) a 10" speaker specifically designed for bass guitar (old Traynor speaker cabinets are very cheap in local music stores - most were originally stuffed with undistinguished Marsland speakers which have subsequently died).
The amp still has its original power supply capacitors - I may update this. It is the later cabinet design with a removable top. The circuit diagram was missing from the underside of the top plate - I have already sent a letter to Yorkville asking for a schematic.
I would be delighted to hear comments and suggestions from other YBA-3 owners
Now only those with Super Custom Specials can kick sand in my face!Two more people have joined our ranks, but I a was a bit slack with the record keeping so I have no idea who they are!(Things have been a bit hectic here...)
I just bought a Studio Mate and have been completely blown a way by it. What a great little amp! The "treble boost" is the secret weapon IMHO. Chords positively *shimmer*...
As for getting yours serviced, any decent amp tech should be able to help you out. I don't think there's anything special or tricky about Traynor's circuits.
Good tubes will make a huge difference in the Studio Mate. Mine still has the stock(?) British 6BQ5's and 12ax7's in it (I think this amp had been sitting in a closet for 15 years...). I have no doubt they're a big part of this amp's great tone...
I haven't had much luck finding good NOS tubes in Canada (anyone?), but can you can try these US suppliers for good quality EL84's:
www.angela.com www.tubesandmore.com www.triodeel.com www.stf-electronics.com www.vibroworld.com www.flabby.com
Check 'em all out, 'cause selection and prices really vary. I believe all of these dealers are reputable. Anybody recommend others?
Other comments/observations re: the Studio Mate.... Very nice reverb. Great tremolo. The four 8's sound really good...tone ranges from very hi-fi to nice and punchy. Surprising bottom end (closed cabinet?). I don't really like the way they break up.... a little too brittle. I'm also afraid of blowing them. I bet replacements would be impossible to find! Anybody know who manufactured these speakers? Replacements?
Let us know how you make out with your Studio Mate Mike...
Stevie Rob
>Are these like major Wattage 4 El-34's ...WHat are they getting for YSR-1's
Yes - the YBA-3 have an EL34 (6CA7) quartette run at 540 volts putting out about 150 watts. Traynor made a guitar amp with the same form factor (almost 27 inches wide) but with lower voltage that produces close to 100 watts out of 4 X EL34. The YGL-3A lacks the power of the YBA-3, but it has two channels with independent tone controls, plus reverb and tremolo. The two amps usually sell for about the same price. I think a YSR-1 is worth more than a ordinary Bassman (YBA-1), but less than a Mark 3 (YGL-3A). I don't see many YSR-1's in the stores - there are far more Bassmasters locally. Below are some prices from Songbird Ottawa's web site. They never have bargains on Traynor amps anymore - Songbird is too familiar with them.
>Traynor tube bass head '60's/50 watts Bass Master good $253 - looking for a great Bassman style head? This is it.Great guitar head or studio/home bass head. We have two in stock.
>Traynor all tube 100 watts head early '70's? YGL-3A Mark III exc. $396 - with reverb and tremolo
The other thing I notice was that the trem did not seem as deep as others that I have heard.
Thanks again Bill
>... the cap coupled reverb circuit in Traynor amps works very well I find ... and it shouldn't be hard to fix ... make sure the 15K (I think) resistor on the 5bq5 plate is rated for 10 watts in case it's missing ...
Someone mentions the speakers in these were crappy...I guess I have to agree although the ones in the amp are not hammered. I tried it into a 4x12 cab with a Fabtone pedal in frint of it and it had a very nice glassy sort of overdrive.
I got it with the back held on with only 2 screwa and packages of Radio Shack resistors and such taped to it... After messing about for a half hour or so it was pretty obvious that someone was trying to make it into a high gain master volume type dealie...I figure I was in for some pretty serious repair work ...I undid all that was not obviously original cleaned it up and Bingo it came right back from the grave like a good little amp... Needless to say I did not have to pay a king's ransom, but it still needs some help....It is the victim of some poor repairs but it wants to be heard, I suspect it takes a lot to put a traynor in its grave.... Bill
JC I pulled the lid off the studio mate although I only had a minute to look at it....I saw some resistors in the vicinity of the reverb cap tube that had been replaced with rather fresh looking 1/8 watters. When I get more time I will look at the schemataic and see what's gone on inside there. But I would think your comments make total sense to me and that a filed resistor would definitely cause the problem. Thank you greatly....
I was curious if you thought the Traynor reverb when working correctly was as good as a transformer driven circuit. It seemed so bizarre to drive a low impedance reverb driver with a capacitor coupled circuit. Maybe I just do not understand it that well. Could the high frequency response of the cap circuit actually be better ????
I also noticed that the tubes seemed to run very hot with the amp cranked up so I thought it would be nice to add a bias adjustment. Any body got suggestions on this one.
I was checking out your page on Traynors. Thanks for the schematic! I was wondering if you would know what kind of transformer would be suitable for a replacement. I heard Hammond made their transformers. I'm guessing 300 VAC with 6.3 V taps of some big amps. If you have a model number or specs, I'd appreciate it!
Thanks, Matt Warren
JC I checked the 10K resistor that you mentioned in my studio mate and found it had been replaced with an 1/8 or 1/4 watter and was pretty well hammered..Nice call ...It looks like many of the resistors have been replaced .
I got my YSR-1 today It looks very rugged and is generally in OK Condition.
The pots and connectors seem dirty. The Grill cloth is frayed in spots and stained Anybody know where to get this style cloth ??? Any input on best way to restore pots...Did this use linears....Thanks for the informative web site on Traynor amps. As a new owner of a YGM-4 combo, I'm looking for info on it. Any other sites you can recommend? Also. can you tell me the difference between the Guitar Mate (YGM#) and the Studio Mate (YGM-4)?
Jeff Ford
Hi,
I picked up my second Custom Special. It's been some 30 years since I bought my first one.
The 'new' Custom Special is either a 1971 or 1972 model - the inscriptions are somewhat contradictory. I am impressed with the upgrades - internal fan, removable top for servicing, Marshall style up and down inputs, real 6CA7 tubes, metal grillwork and master volume. All pretty innovative stuff for an owner of a '66 Custom Special with 7027As (converted to 6550s). This may take a little getting used to.
Except for a little surgery to the Treble Boost and the finals protection circuit, the amplifier is stock. A cap job may be in order soon and I'll probably be on the hunt for N.O.S. 6CA7s.
This feels a little like buying the new VW. OooooWheee
Terry Ladd
I've also been able to pick up my second YBA-3 this last week. It sounds identical to Terry's, except for the metal grill(mine is standard grillcloth over wood). Internals are completely stock but I do have a question I'm hoping someone on the list may be able to answer.
I would like to convert my non-master volume YBA-3 to run 6550 power tubes. I've done research thru the usual channels, and it appears to be a potentially easy mod, easily reversed if I don't like the results. Can anyone offer up the procedure you or your tech have used to make this conversion? My take is that I need to increase negative bias voltage for the 6550's and may have to rewire tube sockets due to pinout configuration differences with the EL-34s currently in the amp.(This opinion was developed using schematics and conversion data from Pittman's "Tube Amp Book, Vol. 3".) -What am I (or Pittman) overlooking? Sure dont want to fry anything.
-For those who have done this...How do you like the sound? I envision SVT round...
-currently in the amp, power tube socket pins 1 and 8 are connected together, then to ground. I think this connection may support the 6550 direct plug in, no mods required here. Comments?
Thanks to all in advance!!
Any inputs on this would be greatly appreciated.
Thanks,
Mike
Why, Soitainly!!
>I would like to convert my non-master volume YBA-3 to run 6550 power tubes.
You do not HAVE to do any rewiring to the sockets. However, you insert a 1R to 10R resistor between pins 1+8 and ground. This allows safe measurement of Ik and also acts as a fuse for each tube. You should also add 1k-5W screen resistors for each output tube. This extends tube life immensely and accommodates ANY grade or type of tube (and anyone who doesn,t is asking for trouble).
The only thing you should check is that the bias range extends to -70V or -80V. You can do this by unplugging the output tubes, then sweeping the bias pot for the maximum negative voltage on pin-5.
If this voltage does not reach the -70V mark, then you will have to change a resistor in the bias network. The 150k-2W could be changed to 120k-2W or even 100k-2W. I have seen paralleled 150ks here! Or you can change the resistance between the 15k and the bias pot (or between the bias pot and ground, depending on vintage). Increase whatever value is there. Then recheck the bias range as above-- NEVER with power tubes in.
Once you have confirmed that the bias voltage can sweep to this more negative range, then you can plug in some tubes.
Tone is rounder and more full bodied. Enjoy Kevin O'Connor
Hi: I recently purchased a Studio Mate combo amp and I'm looking for any information on it that others may be willing to share. I plan to build a new cabinet for it and either rebuild it to stock or mod it a little for a nice EL-84 based project amp. Any info appreciated. Thanks. JeffI have a Studio Mate Combo as well ....when I got it it was not working and gradually I have fixed it up.....changed caps etc...removed bad mods and it sounds pretty darned good as built ...I especially like the sound of it driving a 4 x 12 cab... Bill
I just bought a Reverb Master YRM-1, with the 2 x 15 cabinet. Can you tell me anything about this amp?
Thanks!
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dirk Spencer
>I have a question. If you read on you will find it close to the end somewhere.
>I have a Traynor YGL 3/3a Mk3 (or something close to that). Anyway, it is 100W with two essentially clean channels. One channel has a reverb and tremolo. I needed an amp with some distortion so I put in an extra ECC83 and used one triod as an extra gainstage. I also moved the tone-control to after distortion and cathod-follower and made it marshall-fenderish. Possibly, I also changed some other caps. I don't remember, it was a year ago. Anyway, this gave me a channel with a rich and pleasing sound for blues and rock. But, I cannot take it up to "metall-distortion" because of squeaking. I have attributed this to the physical layout of the amp: all passive components are placed on a cardboard strip running through the center of the chassis. So I am planning to get rid of the cardboard by the preamptubes and make a more localized layout. Since this would imply a certain amount of work being done my lazy personality keeps this on a planning stage. ;-)
>Now, compared to my modded channel the original clean channel is almost useless: cold and thin. So I had a look at it with a scope and a signal generator. (to little bass and too much high frequency, my opinion) I found that the sinus curve looked digitalized. Not in the way that it had steps but the curve looked like it consisted of short straight segments. After some fiddling with the bright-switch I found that this was really because of a weird looking signal of smaller amplitude and higher frequency that was superimposed. I do not remember the exact frequency but I think it was somewhere between 10 and 20 kHz, i.e. well above what the speaker can reproduce. Does this phenomenon sound familiar? Is this a feature of the construction, cardboard mania again? I find that hard to believe. >My plan for this channel is to put in yet another tube and make it a bassman. That would also allow a connection to the reverb. >I have already installed a foot-switch controlled relay-channel-input-swapper.
>Comments, opinions and advice is welcome. To cardboard or not to cardboard, that is the question. /Olof Westman westman@tp.umu.seI do not know exactly about the YRM-1 but I just got a YSR-1 which hase for 1/4 inputs two channels and two El-34's with reverb and trem....I cleaned it up all the pots jacks etc replaced a hand full of coupling caps with Orage Drops and then voiced the two channels via cathode bypass caps and different value coupling caps .....I revoiced it so I could cross patch the two channels and then mix them like folks do with the older 4 holer marshalls.
So last night I hook up the YSR-1 to 2 Jbls 12's and with my tele (Jerry Donahue Bridge Pickup) Its got the greates edgy grindy distortion I had heard short of El-84 based (Maybe EL-86 as weel) so I get to thinking this thing was suppose dto has a real clean sound like fender and JBL's but what is happening... Rather than say the revoicing was a failure I got fascinated and thought I would run with the madness (serendipitous ???). So I try a couple of guitars 79 strat etc....Tele w/ jd Bridge and Humbucker in neck has more moves than a french H**ker. SO i find a slow deep trem setting that I like and crank up the verb and say hey hey!! so now the YSR-1 is sitting on top of a STudio Mate combo and theres one hole open on the YSr-1 and a 12" patch cord (orange high visibilty) so what would you do.....Plug that last hole up with a jumper and I say hey that's cool so let say set the reverb and trem about the same so I play some stuff and am happy for a whole 15 minutes when the thought occurs well theres now another empty hole now on the STudio Mate so what would you do.
So while I am playing I looking around and all I see is another nice 10 to 12 foot Guitar Cable....So then as we play we have to ask the Question ...How did the Univers get started but that's not really the question we wanted ....Ok so what is around 10 to 12 feet away fromm the Mate and we end up spotting a Black Vested Jcm 800 2203 sitting on top two Matching 4x12's onw 400 watt and one 320 watt vintage 30 cab....so the only unanswered mystery at that point is which hole to plug in the 2203....well lets not be to hasty so you play futz around with the four tone controls and the phase rev on the humbucker and think go this is great the reverbs and trems are close but not locked so they are going in and out of phase ...hmm....try to get a rythem going around the diffrrence ...oh yeah more fun ...but wait ...it its light a Blinding Flash ...THIS HERE SOMA BITC* COULD USE SO HARD TIGHT BOTTOM END...ok so we now discover its a moral imperative to put down the tele pick up the cable and jack in the 800 and then add some massive bass..... Can't wait....fire up the Marshall plug in the cable and dial up the settings figured everythings about as outrageous as it can get so we should jack the low input into the 800......and boys and girls I fall to pieces when Ipick up the tele to begin going where no man has gone bfore and nobody's home in my bottom end.... Well I am jonesing for a tone fix so I aint't putting it down this time until Ford has a better Idea.....whilest playing a little La Grange STyle ala Boogie a weasel over far enough to my surprise I see and empty hole or two behind the YSR-1 and a little sign that say DI so I figure that hole needs to be plugged and take the cord from the Mate while holdin a big open A chord and quickly out of one and into the other....Now we are getting a read on the Richter scale ....OOOOO YEA now It really happening... so having oh I am happy exploring this for oooo 15 minutes and then I realiize the reverb and trem are coming out of the stack and almost chorusing against the ohter pile of stuff a ways away....so it occurs that we migh want to crack the valves on a bit of mids and highs in that ole' 800 as it wants to verb and trem....damn its coming right out of the DI for the YSR-1 ....... When the ashtray finally worked it way off the table and onto the floor...I knew I had taken care of the Tone Jones...... I was just going to practice a little....
I have an early Bassmaster and I want to replace the caps in the power supply. They are the mallory twist-lok type. Does anybody have any suggestions as to the best cap to use and where I can get them?
Thanks in advance for your help.
Best Regards, Dave Tomlinson
I have found a "Traynor Guitarmate Tremolo III." I've only seen one other tranor amp and were wondering if they were any good because this one seems like it is a steal. My guitar tech. didn't know anything about them either. I'd appreciate it if you mioght could give me some info.and an estimate of what it is worth if it is in pretty good condition.
Thank You,
Clint Cryer
Well, my original posting was a question on whether it would be a good idea to remove the fibreboard (at the preamp only) and use "point to point" instead. This technique allows for compact and highly localized circuits and is thus optimal for high-gain mods since (err....) capacitive proximity coupling resulting in undesired feedback can be kept well under control. On the other hand it takes alot of work to make the change.
Kevin quickly answered me that I should keep the board and that he had been succesful in making mods with a lot higher gain than the one I had in mind (3 triodes) without having to go to point-to-point. So I made something in between: I kept the board but put as many components as I could directly on sockets and pots. e.g. EQ caps on to the pots and those gainstage-follower stages can be built entirely on the socket if its the kind of socket with a little metal cylinder in the middle. I more or less had to do this anyway since I have put in one extra tube for each channel and there were no place for the extra components needed.
With this technique I had no problems in making a straight 3 gain-stages channel. Unfortunately, it seems that the feedback, I had previously, was in part responsible for creating that lovely crunch. I guess it worked as some sort of non-obvious active filter. (as long as it didn't squeek of course. nothing lovely about that) So I cloned a 2203 preamp instead and included an effects-loop output. This could also be used for overdriving the other channel allowing for effectively a 4-gainstage channel. - ... Well, yes, the squeeking came back again. Two main reasons: a microphonic tube and the reverb driving EL84's output cap. Now, that cap sits in the middle of the board and radiates it's signal to everything nearby. This is on the verge of being a faulty design (IMO). Even in stock condition it is possible to get unexpected notches in the signal if the amp is fed a strong signal, e.g. from a tubescreamer. This seems to be because the wire to the second stage of the "reverb double-triod" passes close by the EL84 output cap and picks up something undesirable. I rearranged components on that side of the cap and put in a screening plate(grounded) to the right. No more squeeking! Reverb sucks however. It is a high-frequencies only reverb and the original filtering appears insufficient to deal with the bass-rich signal from my bassman-like clean channel. Also the circuit was obviously not designed to receive a heavily distorted signal. With the master-volume at zero I could hear the springs of the reverb going nuts from the mass of high frequencies. I put a cap over the EL84's grid resistor to filter the extreme highs and halved the input signal with a resistor to keep from overdriving the springbox. Well, the reverb became better but it still sucks. Any ideas would be appreciated.
/Olof Westman>I have found a "Traynor Guitarmate Tremolo III." I've only seen one other tranor amp and >were wondering if they were any good because this one seems like it is a steal. My guitar tech. didn't know anything about them either. I'd appreciate it if you mioght could give me some info.and an estimate of what it is worth if it is in pretty good condition.
>Thank You,
>Clint Cryer
>HR>Some weeks ago there was a discussion on power ratings of various traynor amps. So I am a bit late but I have a Mk3 (YGL-3A) and have never believed it to be 100W. I have had some trouble with a blaring quality in the sound and so decided to have a look at what the power stage does.
I live in Sweden and the mains voltage is 220V. The amp however is rated "240V 1.5A". And so I am not surprised to find that the B+ voltage is only 407V (rather than 436V). With this plate voltage the 100W is theoretically changed to something like ~87W. However my amp was putting out only 65W through my 4ohm 4x12" cab. Measured just before clipping. The B+ voltage was now only 380V something. Making some consideration (guessing and praying, after all the voltage was 10% below specs and the trafo looked massive) I decided that it would be safe to double the filter cap. (My judgment only, I do not recommend it). Only 40uF for a 100W amp seemed a bit on the cheap side. This raised the output to 72W. Then I put in some new (err... newer.. ahum..other) tubes and rebiased and got some 80W out of them. Fully clipped output was almost twice as high, around 150W. (My 4ohm resistor makes a lot of noise when putting that through ;)
Eventually I decided to make use of the lowered B+ voltage and biased the tubes slightly warmer than recommended. This made no change to the power but the transition distortion was decreased.
Enough about power. My real objective was to look at the frequency response. Well, lets start at 50Hz and consider the amplification of total stage including output transformer. (In stock, without the changes mentioned above. Not it matters) Raising the frequency slowly increases the amplification until 700Hz where the amplification has risen with some 5%. >From then on the increase is faster and at ~2.5kHz it saturates at about 25% higher than the 50Hz level. (25% in amplitued means 56% in power)
Although this frequency response would explain why the amp can be experienced as a bit cold I found nothing that could explain my blare-problem. I guess I have to blaim the speakers then.
/Olof Westman
I just received three Custom Special schematics from Yorkville Sound. (Their current address is: Yorkville Sound, 550 Granite Court, Pickering, Ontario, Canada L1W 3Y8.)
They are (using Yorkville's scribbled titles): (1) 'Very first model using 7027A's', (2) 'Pre-Master Volume Control', and (3) 'Final with Master Volume'. I have made 300 dpi scans of each of the schematics, and will email them on request. I will also send them along to the Traynor Amplifier Schematic Archive, but as JC already has at least one YBA-3 posted, he may not wish to add these.
There are some interesting differences between the models:
'Very first model using 7027A's'Ê (YBA3_1.GIF 92K) ÊÊÊÊÊÊÊ Transformers ÊÊÊÊÊÊÊÊÊÊÊÊÊÊ T1 PowerÊ 79691 ÊÊÊÊÊÊÊÊÊÊÊÊÊÊ L1 ChokeÊ 58347 (Traynor Signatures also used filter chokes) ÊÊÊÊÊÊÊÊÊÊÊÊÊÊ T2 OutputÊ 79692 ÊÊÊÊÊÊÊÊ Tubes ÊÊÊÊÊÊÊÊÊÊÊÊÊ 7027A X 4 ÊÊÊÊÊÊÊÊÊÊÊÊÊ 12AX7 X 3 (but only half of V1 used) ÊÊÊÊÊÊÊÊ ÊÊÊÊÊÊÊÊÊ Bias: Not adjustable, -46 V indicated on diagram ÊÊÊÊÊÊÊÊÊ Date: Jan 13, 1967 (musically a very good year!)
'Pre-Master Volume Control'Ê (YBA3_2.GIF 161K) ÊÊÊÊÊÊÊ Transformers ÊÊÊÊÊÊÊÊÊÊÊÊÊÊ T1 PowerÊ A 1315ÊÊÊ (400-0-400 V RMS) ÊÊÊÊÊÊÊÊÊÊÊÊÊÊ L1 ChokeÊ replaced with 470 ohm 10 watt resistor ÊÊÊÊÊÊÊÊÊÊÊÊÊÊ T2 OutputÊ A 1316 (8 ohm) ÊÊÊÊÊÊÊÊ Tubes ÊÊÊÊÊÊÊÊÊÊÊÊÊ 6CA7 X 4 ÊÊÊÊÊÊÊÊÊÊÊÊÊ 12AX7 X 3 (but only half of V1 used) ÊÊÊÊÊÊÊÊ ÊÊÊÊÊÊÊÊÊ Bias:Ê Adjustable, -50 V indicated on diagram ÊÊÊÊÊÊÊÊÊ Date:Ê Guessing based on the revision codes, the 6CA7 version was ÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊ designed on Dec 11, 1968 (the original model lasting 23 months).
'Final with Master Volume'Ê (YBA3_3.GIF 153K) ÊÊÊÊÊÊÊ Transformers ÊÊÊÊÊÊÊÊÊÊÊÊÊÊ T1 PowerÊ A 1315ÊÊÊÊ (400-0-400 V RMS) ÊÊÊÊÊÊÊÊÊÊÊÊÊÊ T2 OutputÊ A 1332ÊÊÊÊ (8 ohm - changed part #) ÊÊÊÊÊÊÊÊ Tubes ÊÊÊÊÊÊÊÊÊÊÊÊÊ 6CA7 X 4 ÊÊÊÊÊÊÊÊÊÊÊÊÊ 12AX7 X 3 (all of V1 used - an extra gain stage) ÊÊÊÊÊÊÊÊ ÊÊÊÊÊÊÊÊÊ Bias:Ê Adjustable, -50 V indicated on diagram
ÊÊÊÊÊÊÊÊÊ Date: Guessing based on the revision codes, the master volume version ÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊ was designed on Dec 2, 1970, the last revision was April 18, 1974.
(If you are using the bias adjustment scheme suggested on the schematic -Ê voltage drop across the screen resistor - be careful you have the right model. Early 6CA7 models use a 470 ohm 10 watt resistor and expect a 4 volt drop. Later models [ from July 18, 1971] use a 1Kohm screen resistor and suggest adjusting for an 8 volt drop.)
The master Volume is a simple volume control acting between the preamp output (V2B) and the phase inverter/driver stage - V3. All the amps have the same controls with the exception of the master volume.
The 6CA7 models offer an alternative English power supply, the earliest model does not. Perhaps none of the 7027A equipped models were sold in England.
There are many detailed changes between the circuits that I will not attempt to describe (or even understand, for the most part!)
Eric