'57 Guild Model 66-J........

59Panhead

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I posted this over on the Hoffman Amps site, and a member there pointed me here. Forgive me if I don't re-type all that I posted. I will paste from there:

I just took delivery of a Guild Model 66-J amp, on Monday (16Dec13). Before I purchased it, I searched for a schematic and found only one original. But, I did find Steve Luckey's nicely drawn schematic, the same but much better. Tuesday, I put it up on the bench to bring it up on the lamp limiter. I had been forewarned that the fuse block was broken. It's one of those little ones, that holds the glass fuse in two clips, mounted inside on the chassis. One clip was gone. I'm thinking to myself that this is going to be an easy fix. I jumper the two wires together, as my limiter has it's own fuse holder, with a 3 amp fuse installed.

So, it's on the limiter, and by the time I'm up to a 100W bulb, I notice the first resistor in the power supply is starting to get hot. This is definitely not the first time that's happened, because it's a 3 watt resistor and the color bands are cooked beyond reading. I start checking the amp against the schematic (original and Steve's), and my amp doesn't match. Mine is a 7 tube, and the schematic is for a 6 tube. The insides of this amp have all the appearances of not being touched, and everything looks original to the amp. I make a quick check of DC voltages throughout the amp, knowing they will be low. I have high voltages where they should be, so I power it down.

Frustrated, I begin the slow process of drawing a schematic from scratch. I decided to make a layout drawing of the whole amp, including the chassis. That way, I can have it on the screen while I'm making a schematic. Between my multimeter and my capacitor tester, I came up with all the values, though a couple are questionable. I indicated those on the drawing, the cooked one being one of those.

All pots are 1M in value, and dated to '57. There is a 12" Jensen dated at '56, and two small speakers (maybe 3" each) paralleled to each other, date not determined on those. Speakers appear to be original to the amp, or at least as old as the amp. The 12" has a DC ohms just a little above 6. The two paralleled have the same. So, each load can be considered as 8 ohms impedance. For now, I'm assuming their connection to be at two different 8 ohm taps.

I completed the schematic, along with the layout. I made the schematic very spread out, to be easy to see, and to go back and make it look a bit better. But for now, it's good to have something to troubleshoot by. The configuration is a departure from what I'm used to seeing. And maybe it's just the way I have it drawn.

As a final step before troubleshooting, I put my auto-transformer on the primary of the OT and connected a meter to the primary and secondary. I eased the voltage up to 30vAC, and saw nothing on the secondary. So, I shut it down and disconnected all. I took DC resistance readings of the primary and secondary. The primary is open. No resistance at all. The secondary has low ohms, but I forget what they were. I've got to purchase a replacement, though this one has four leads on the secondary. One lead was taped back. It's color may originally have been red, but it's too faded to tell. The other three leads are also too faded to tell their color. I'll go back and check the primary again with my Meggar set for 500v. I forgot about it earlier, when I was in the amp. That will prove an open real quick. I'll make resistance readings of the secondary, to have some idea of what I'll need for a replacement.


I made my drawing and physical layout as a CAD drawing and plotted it to a PDF file. I don't see a means to upload it to the site. If someone can show me, I will do so. It's not a very large file, but high resolution for zooming in close. The output transformer is a Dongan A393 embossed in one of the side covers, and the number 27291 stenciled on the top. I emailed Dongan, but won't hear back from them before next week (maybe). I'm thinking that they no longer manufacture audio transformers. None are on their product list.

Here are a couple pictures:





So, this one is at a standstill, until I can find a replacement OT. There may be other issues. I'm thinking that I will pull the power tubes and see how it powers up without them in the circuit. Something is smoking the first resistor in the power supply. There'll be more to come.

Have a good one.

Jack
 

Jeff Haddad

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I'm afraid I don't know enough to offer any help, but that is a great-looking amp! It looks like the only wear is along the bottom. I'd love to see more pix and follow your restoration progress.

Is that a DeArmond tremolo unit on the bench there? Nice!
 

mavuser

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just wait for Default to come along and post (Steve). I just bought the same amp and he will likely get his hands on it at some point. 1957! amazing right.

but yours has those extra little speakers in it, and you say an extra tube. does it say 66-J on it anywhere? got a picture of the top? mine says 66-J on the top, and Guild/Masteramp on the front. looks like yours is missing the Guild/Masteramp badge.
 

Default

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Saw (and commented) that on the Hoffman board. For those who don't visit there, this is an example of how there is no such thing as a standard Guild amp. This one looks like like the same vintage as my Masteramp with the transformer bolted to the cabinet. It's almost like the head of amp manufacturing, Ralph Sanders, was just trying to figure how to design an amp.
The tremolo circuit has a 12ax7 and a 12au7. I'm not sure that the 12au7 is original, but if it it works, maybe it does, lol!
 

59Panhead

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just wait for Default to come along and post (Steve). I just bought the same amp and he will likely get his hands on it at some point. 1957! amazing right.

but yours has those extra little speakers in it, and you say an extra tube. does it say 66-J on it anywhere? got a picture of the top? mine says 66-J on the top, and Guild/Masteramp on the front. looks like yours is missing the Guild/Masteramp badge.



I plan to remove the handle and put something as close to original back on it, as soon as I find a picture of such.
 

59Panhead

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I'm afraid I don't know enough to offer any help, but that is a great-looking amp! It looks like the only wear is along the bottom. I'd love to see more pix and follow your restoration progress.

Is that a DeArmond tremolo unit on the bench there? Nice!

Yes, it is. And, in very good working order:





With the help of Dan Formosa's great website:

http://danformosa.com/dearmond/

Check out his other links to this unit.

Jack
 

59Panhead

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Saw (and commented) that on the Hoffman board. For those who don't visit there, this is an example of how there is no such thing as a standard Guild amp. This one looks like like the same vintage as my Masteramp with the transformer bolted to the cabinet. It's almost like the head of amp manufacturing, Ralph Sanders, was just trying to figure how to design an amp.
The tremolo circuit has a 12ax7 and a 12au7. I'm not sure that the 12au7 is original, but if it it works, maybe it does, lol!

I have not spent time studying this circuit, as it was a challenge to get it into a drawing. My V4 is a 12AX7, and pulling duty as the oscillator. V3 is a puzzle, at a glance. I'm wondering if they are attempting a Vibrato circuit (pitch shifting). But, I just haven't had the time to look it over. The 12AU7 was probably there for a reason. When I do have the amp up and working, I can experiment with various gain tubes of that family, and see the effect. I'll post all results here.

Jack
 

59Panhead

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Also meant to ask, it anyone can shed some light on the output transformer specs, I'd truly appreciate it.

Jack
 

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As far as I can tell, it's just a leather handle. Did you check out the Guild amp sticky? The 40-T seems to be the only Guild amp with a suitcase handle. Everything else has a leather strap until Thunder series.
 

Default

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From my one conversation with Aaron Newman, the Guild amps of the time used a lot of material purchased in electronics surplus shops. Aaron said that when he got there, the amps were almost direct copies of Ampegs and they bought a lot of transformers from Todd Transformers. I suspect that they didn't push the envelope on voltage, so whatever the tube sheet recommended would have been what they used. 8-10K plate to plate, probably. Certainly whatever was on sale. ;-) Aaron said they guy in charge of the amps was more of a mechanic than an engineer, so that might explain the tremolo circuit.
 

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As far as I can tell, it's just a leather handle. Did you check out the Guild amp sticky? The 40-T seems to be the only Guild amp with a suitcase handle. Everything else has a leather strap until Thunder series.

Like this one on my (then bluesypicky's and now fixit's) 66-J?

 

59Panhead

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I was hoping to find a way to upload my CAD drawing of my 66-J, but I don't see a means to. If anyone needs a copy, I can send it by email, as it's plotted to a PDF file.

Jack
 

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Way back some time ago, I bought a replacement aftermarket Fender (tweed) Deluxe handle which fit perfectly on my 66-J...looks like Dave's but with rough gray tolex and silverish fretcloth...by pot codes mine has to be a '63.





Original handle was black, but I took what I could get...
 

Bill Ashton

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The guy with the Italian-accent above is also the one that got the tremolo in mine working again, so he is familiar with the circuit. I cannot tell you specifics, but mine has three 12Ax7's, each half of one is the preamp for each channel, one serves as the phase inverter and one serves completely in the tremolo circuit. It is also said these amps have a Baxendall (sp?) tone circuit if that is any help to you. I do have a copy of the Guild factory schematic which was stapled inside the back cover, but not sure one of my vintage would be of help to you.
 

59Panhead

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The guy with the Italian-accent above is also the one that got the tremolo in mine working again, so he is familiar with the circuit. I cannot tell you specifics, but mine has three 12Ax7's, each half of one is the preamp for each channel, one serves as the phase inverter and one serves completely in the tremolo circuit. It is also said these amps have a Baxendall (sp?) tone circuit if that is any help to you. I do have a copy of the Guild factory schematic which was stapled inside the back cover, but not sure one of my vintage would be of help to you.
I would appreciate a copy of it for my schematics library, if possible to send a scanned copy.

My 'extra' tube turned out to be the oscillator for the Tremolo. Both triodes paralleled. No idea why this was done, as one triode would have worked nicely. There's another part of the Tremolo circuit that I've not studied yet, but I'm wondering if they weren't trying for some form of Vibrato. Until I install a replacement OT, and am able to confirm that the rest of the amp is sound, I won't know if the Tremolo works. The very first resistor in the PS is for the most part cooked beyond reading the color stripes. It measures a very high value from the standard schematic.

As to the Tone Stack, mine is a true Baxandall, though once again, all component values don't match the standard. Another reason to have an actual schematic like your, for comparison. The one in the standard schematic is, too, a Baxendall.

I just sent you an email, so that if you want a copy of my schematic, just reply to it and I will attach one. The same goes for anyone who would like the same. Drop me a note by email, and I will reply back with the attachment. Have a good one.

Jack
 

SFIV1967

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I plan to remove the handle and put something as close to original back on it, as soon as I find a picture of such.
I guess the handle used to look like this: (picture from member Zizala)

IMG_0531.jpg


Ralf
 

59Panhead

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Ralf -

What year is the amp in your picture? It has a full back panel, where mine has a top panel, and a bottom one. Also, that one has a Tremolo selector, where mine does not.

And, I'm seeing screws on the strap hold-downs. I was thinking that I would have to drill out the rivets on mine, and the picture confirms that those have been removed. Good picture. Thanks.

Jack
 

59Panhead

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Thanks. I have a copy just like that one, but it is only a 6 tube model.

I have made it a habit of 'rescuing' orphaned amps, over the past few years. Many makes and models. Most are back in working order. Quite a few are still waiting their turn. It's these strange variations, like I seem to run across from time to time, that move to the forefront.

Do you know if the amp that you have pictured has a schematic that can be scanned? The schematic from the link does not have the Tremolo Selector, so that one would be good to have on hand. It probably has differences from the standard and mine. Thanks again, for the info.

Jack
 
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