Guild Thunder T1-12

[Csquare4]

Hi folks,

I just won on ebay a Guild Thunder t1-12, which seems to be in decent condition. I have been looking for a while now to get an early 60's Guild amp at a decent price that was in pretty good condition.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=360381729848

Figured ~$200 shipped wasn't too bad a price, especially if most of the work is done and it is in as good of shape as it appears. They have a 7 day "no questions" return policy, so we will see.

I will have it in a few days I suppose to check it out. I am interested in hearing how this thing sounds, based on the descriptions I have found, maybe it will be a bit like a low power version of my Music Man 65, clean and bright. We will see on that.

Anyways, I like to mess around with my amps and make sure its tuned up. From the description it seems most of the "necessary" caps have been replaced. I will be checking those against any schematics I can find. I noticed through a search of this forum there are a couple schematics floating around, if anyone has one that they can email me, please let me know and I will shoot you a pm with my email address. Also, I am interested in insight as to where to find some NOS tubes for the power section, the 6GW8's. These are new to me.

There is a pretty thorough thread here from a few years ago, too bad most of the photos are dead. http://letstalkguild.com/phpBB2/viewtopic.php?f=7&t=10415&hilit=Thunder+1
But there is some good discussion there. I spent the better part of the morning reading that thread.

Anyways, I think it will look good next to my '63 Polara.

There is a thread about the Polara here, if you want the juicy details... 8)
Anyways, I hope it sounds as good as it looks, and if anyone has a decent set of schematics and some ideas about finding a new set of power tubes, please let me know.

Craig

 

[Brendan]

Nice score! You know, I think I deleted some of my Photobucket pics recently as well and didn't even think about the links to this thread. Sorry if I blew a few away. What a fun project that was and what a great amp! I think the Cannabis Rex warms it up a bit. I actually have mine up on Craigslist right now to see if I can get any interesting old amp trades. I'm itching to work on something. If no good bites, I'll keep her. It's a shame they don't have a decent market value.

Love that guitar!

 

[capnjuan]

Hi Craig and congratulations on your new amp! I agree with Brendan ... if everything checks out, I also think a new speaker would be the next thing. PM sent re/ schematics. j

 

[fearless]

Congrats on the amp. That Polara is a stunner.

 

[Csquare4]

Thanks all for the comments and the help. I told Capn Juan I would update the thread with photos once I get it in house. I may even draw out the schematics if it is radically different from the ones available. So please stand by.

Craig

 

[Csquare4]

Update -

I received the amp, what a great job they did packing. Anyways, so the amp arrived in great condition. I unpacked it, tubed it up, plugged it in (2-prong, more on that later) and powered it up. At first the front panel light didn't come on, I thought - "oh no...here we go" so I looked in the back at the tubes and the heaters were glowing, so by the time I looked back at the front, well the light was glowing. So, yeah, I remember reading about that "feature" somewhere, ha ha.

So here is the amp. I told a few guys that were interested that I would post some photos. Some of these may be redundant, but I like to have very clear photos of the circuit side of things for future reference so I took plenty. I guess I might as well share. The amp still has the 2-prong AC cord with the Death Cap intact and original tubes (at least the 6GW8's anyway). The 12AX7's are both Sylvania's which seem to have some life left, but the power tubes, not much...they are definitely long in tooth. Even though the Ebay add said the Electrolytics were replaced, I guess they didn't notice the big-a** can on the top of the chassis with the 4x 40uF caps in it, ha ha. At least the date code of the cap can matches the rest of the amp. Oh well, that's on order with AES...

Here it is in the jam room, getting ready for the first run.

So, sound wise, it actually breaks up a bit with some singing sustain when it is dimed. That may be due to the "original" cap can on the B+ filtering. The tremelo is pretty weak and deadens the sweetness of the dry tone. I will look into that a bit, but it may just be the unique circuit.

Close up of the front panel. Still in decent shape. All the pots sound good.

Original '64 CTS speaker. This thing probably needs to be retired if I am going to play this amp much.

Guild sticker - not sure what that is about with the S/N, lol...is it 2203 or 2204? Probably a Monday morning.

So here are some circuit photos - please excuse the redundancy, but this is where the meat and potatoes lie -

V1 and V2 side of the house. The input jack for the "normal" channel is not grounded - yikes, I guess they rely on the chassis for ground? Dunno.

The V3 and V4 PI/Power Tube section...the Cathode Bias resistor is the big "terra-cotta" looking thing hanging off of pin 7 of the tube in the top of the photo. The bias cap is the blue 22uF on the lower tube pin 7. This was replaced by the previous owner, so I am not even sure it is correct as one of the schematics provided in another thread showed this as a 33uF. Maybe they substituted the smaller cap to try to bring a little more bottom end to the output.

This is part of the tremolo circuit with the "depth" pot in the lower right. This can be adjusted to make the trem mix a little wetter (or dryer). I didn't play with it much as I wanted to get a good strong sound from the clean channel first.

One of the power caps that was replaced, which is the most important one I suppose, being the first stage coming off of the rectifier tube. Also, the pot here is the hum balance, which basically adjusts the heater voltage coming out of the PT so that they match and minimize induced hum.

The 2-wire ungrounded AC coming into the chassis and power switch. The yellow "mustard-looking" cap is the infamous Death Cap. That sucker gotta go as soon as I get my new 3-wire grounded AC plug. Which leads me to a story...I was jamming a bit with my son, he was playing through another amp. He was showing me a note that I missed on a new progression he wrote, when he touched one of my strings while his other hand was on the strings of his guitar. He figured out real quick that ain't a good idea. Zap city.

A few more circuit shots from a different angle or for more clarity:

Here you can see the 2 light blue pre-amp bypass caps that were not replaced in the recent "service". These are both 32uF 50v...easy enough.

Another showing the "Bright" switch circuit, which is the thing hanging off the back of the pot. It is basically just a pull switch pot that splices in the little high pass capacitor/resistor circuit.

The top of the chassis to show the tube layout. The 12AX7's are on the right under the cans, the 6GW8's are the two in the middle, and the 6CA4 rectifier is the one on the left above the power transformer. Still pretty clean for a 47 year old amp.

Here is the original can capacitor (the silver cylinder for those that don't know) containing the 4x 40uF capacitors which form the backbone of the power conditioning. This thing has gotta go as well.

Original transformers.

Original "Guild" branded 6GW8 Power Tubes and Sylvania 12AX7's.

So there it is for those that were interested. I still have some work to do before I play it again.
1- Unsolder the output transformer and measure the Turns ratio so I can figure out the output impedance. The tube sheets have the 6GW8's at an incredible 48k output...yikes...typical tube ranges, 6V6, 6L6, EL34 etc. are in the 4k-12k range...this is 4x? Weird I tell ya!
2- Replace that 2-wire lamp cord and ground that AC!
3- Kill the death cap
4- Find some new Power Tubes to replace these originals
5- Replace the 4x 40uF Can Cap and the dropping resistors
6- Replace the 2x 32uF pre-amp bypass caps
7- Try a new speaker...probably a Celestion 25W Greenback is what I am thinking.
8- Start looking at the tremolo if I need to tweak it a bit.
9- Start looking at changing a few of the coupling caps and bypass caps to get some different voicing depending on how it sounds.

So there you have it. Let me know if you have any questions and/or comments. Also, for future readers of the thread, please feel free to PM with any questions...I always hate doing a search and finding a thread that is years old, then not knowing what to do if you have questions. So here I am...shoot me a question. If I am still around, I will do my best to answer.

Craig

 

[fearless]

The amp looks nice. I have one of these, plus a later model but have never found/made the time to give them the attention they need. You are inspiring me a bit to pull my finger out...

One thing though - why replace the CTS speaker? I was under the impression that these are an excellent speaker, one that would justify repairing if there is something wrong.

 

[capnjuan]

@Craig: great pics and you're right, remarkably clean for its age. More after I get a chance to study the pics.

@Fearless: there was nothing wrong with CTS speakers back in the day but over time, all speakers lose efficiency. Any new speaker will out-perform a vintage speaker in terms of converting signal to sound waves ... improved frequency response and accuracy ... more 'presence'.

 

[Csquare4]

The CTS speaker is probably decent sounding, even though it was kind of loose and flabby. I will wait until I get the electronics sorted before I do anything with the speaker...the initial playthrough I had the volume all the way open and was thinking it could be tightened up a bit with a different speaker. Plus, if I ever want to resell it, I would like to keep the original intact. I can see me easily working the speaker pretty hard (w/ and w/o a tubescreamer) to get into the "tone zone" and I have no idea what these speakers can handle. I will play it by ear

 

[Csquare4]

Some additional insight into the output transformer -

I disconnected the OT and wanted to try and figure out the Impedance that the tubes would be seeing reflected back from the speakers with the 8ohm load. Interestingly, the output has a series 120 ohm and 0.1uF in parallel with the speaker outs, which I suppose is there for rolling off the low frequencies hitting the speaker. Dunno.

So, I found out that the turns ratio N=33.2, so the Impedance ratio of the OT is Z=1100 (approx). With an 8 ohm speaker load, the reflected impedance into the tube is 8.8k ohms - which seems entirely normal for most power tubes, but not the 6WG8's...which according to the tube data sheet is looking for about 48k ohm. So, either this is horribly mis-matched, which means it would probably be better matched with a 16 or 32 ohm speaker load, or the RCA tube data spec sheet has a terribly important typo on it. I suspect that the Guild engineers took an off-the-shelf OT and just plugged it in and said "ok, that sounds good"...without actually determining what was the best circuit design. Strange.

Craig

 

[capnjuan]

Hi Craig:

Tremolo: if it were my amp, I'd change out those four trem caps. 7 times out of 10, weak/bad/no trem is one or more of the trem caps going/gone bad ... 2 time out of 10, one of more of the resistors is shot ... 1 time out of 10, it's something else ... switch, pot, whatever. The tremolo oscillator is on whether the trem is invoked or not which wears them out. I'd probably do the resistors too because I have a thing about not opening the chassis any more times than necessary ... and opening up to find a bad $.25 part that I could have changed before ... well :evil: :wink:

Cathode bias: I saw the 6GW8 cathode resistor on one tube and the bypass cap on the other but didn't see a jumper (grey?) between the two pin 7s; I'm sure it's there, it just doesn't show clearly in the pic. You might want to consider using a Sprague Atom 25uf/25V (or 50V .. there's plenty of space) and the same for the preamp tubes.

Guild's oddball 32/33 uf values are not supported in the modern aftermarket. You might find some surplus caps but then they'd have been sitting around on a shelf for a while which could undermine their reliability. Any change in frequency response because of a handful of ufs difference will be undetectable.

OT: Well ... your guess is as good as mine ... I really don't know if a different load would make much of a difference. After all, you're going to get a noticeable change when you switch out the speaker no matter what impedance you replace it with. These amps are only 10 - 12 watts; I mean it's not like the amp is working very hard in the first place.

 

[Default]

The schematic for the Magnatone 411 in the Gerald Weber book, called for a single-ended 6gw8 at 7K-3.2k ohms. Typo on the ratings sheet as you said? :?


As an aside, swapping over to 6bm8's out to be really easy now. 8)

 

[Csquare4]

Tremolo: if it were my amp, I'd change out those four trem caps. 7 times out of 10, weak/bad/no trem is one or more of the trem caps going/gone bad ... 2 time out of 10, one of more of the resistors is shot ... 1 time out of 10, it's something else ... switch, pot, whatever. The tremolo oscillator is on whether the trem is invoked or not which wears them out. I'd probably do the resistors too because I have a thing about not opening the chassis any more times than necessary ... and opening up to find a bad $.25 part that I could have changed before ... well :evil: :wink:

Agreed there, however, these capacitors (the "chocolate" ones), are new and were changed out by the previous owner apparently. I am not convinced they are any good, but I am thinking maybe the tremolo driver tube may be week too, I didn't really roll any known "strong" 12AX7's through that position. I will do that before I button her up again and see if it makes a difference. I may go ahead and swap the resistors while I am in there and possibly upgrade those tremolo caps to Mallory's which I have a pretty good supply of. I will keep you posted on that.

Cathode bias: I saw the 6GW8 cathode resistor on one tube and the bypass cap on the other but didn't see a jumper (grey?) between the two pin 7s; I'm sure it's there, it just doesn't show clearly in the pic. You might want to consider using a Sprague Atom 25uf/25V (or 50V .. there's plenty of space) and the same for the preamp tubes.

There is a grey jumper...you can see it in this photo, from pin 7 under the blue bias cap and tag strip. It connects to the cathode of the other tube and ties them together.

Guild's oddball 32/33 uf values are not supported in the modern aftermarket. You might find some surplus caps but then they'd have been sitting around on a shelf for a while which could undermine their reliability. Any change in frequency response because of a handful of ufs difference will be undetectable.

Also, I do have a pretty good supply of those Sprague Atom 25u/50V so I will take your advice on those. The one's that were previously replaced are 22uF's...they may be fine, but I don't know too much about them...the light blue ones on the 12AX7s definitely gotta go.

OT: Well ... your guess is as good as mine ... I really don't know if a different load would make much of a difference. After all, you're going to get a noticeable change when you switch out the speaker no matter what impedance you replace it with. These amps are only 10 - 12 watts; I mean it's not like the amp is working very hard in the first place.

Yeah, who knows on that. Maybe with a properly matched output section, this thing may even push a little more volume.

 

[capnjuan]

I like Mallory 150s 8)

Okay; didn't realize the trem caps were part of the re-do (I take that back ... what I mean is I couldn't imagine anybody would re-do the trem caps and not the PS caps :? ); unless it's mechanical or the tube, should/oughta be one of the Rs.

Cathode jumper: okay ... just couldn't find it before.

Speaker/output; well ... if you have a 16 or 32 ohm speaker, you're in good shape to test your theory although any newer speaker you put in there is going to sound louder. Of course, that's all after the PS caps ... that's too bad about the seller misrepresenting the maintenance.

I bought a T1 RVT on eBay in 2007 ... the seller said '...might need a few tubes .... " He was right ... it didn't have any tubes and was DOA ... :evil: Good luck!

 

[Csquare4]

Actually John the seller said they replaced "3 Electrolytics" and "4 tremolo" capacitors, so I think they were not entirely misleading. I just assumed when you say you replace electrolytics, you mean the power supply ones, ha ha. Stupid me for making an assumption regarding an ebay auction. So be it, I didn't pay too much for it, what's another $40 in parts to tune it up properly. I would have done that anyway.

Yeah, and on yours, yikes...I would have been a little PO'd. Sorry about that.

 

[capnjuan]

I would have made the same assumption ... <sigh>

 

[coastie99]

Did that amp. come with a footpedal C ?

I have one here of no use to me. And transformers.

 

[fearless]

Hi Gary, you mean 110V transformers, I assume, not 240V?

 

[Csquare4]

Did that amp. come with a footpedal C ?

I have one here of no use to me. And transformers.

No Gary, this amp doesn't have a footswitch compatibility...just the front panel slide switch. Transformers seem fine on mine.

 

[coastie99]

Hi Gary, you mean 110V transformers, I assume, not 240V?

Yeah Skip ..... those Yankee ones.

Output transformer is of course OK for Oz.