Guild Thunder I Reverb T1-RVT

Tubeblaster

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Hi Folks,

I just joined and have been perusing threads about this amp. I have the opportunity to purchase a Guild Thunder I Reverb T1-RVT from the original owner. I have the amp in my possession right now for evaluation. It hasn't been played in 10 years. I heard it at that time and it sounded OK although there was some hum (probably old filter caps). Before that, it hadn't been played since the late 1970's.

It has the two-tone tweed grill and surprisingly; it has a three prong cord. It's serial #6657. It has the polarity switch, which surprised me since it has the 3-prong cord. My buddy told me his parents bought it new for him in 1968 and I don't think any work has been done on it. I can see the 6GWB tubes have the Guild brand on them and are presumably original.

I'm interested in restoring this amp for my personal use. I'm a hobbyist and am fairly well-read on tube amps with some experience helping restore a Fender Deluxe Reverb and a 1938 Gibson EH-150 with a field coil speaker. I did have amp tech help with these projects and may do so again with this amp if I take it on.

I have this amp for 3-4 weeks for evaluation and am favorably inclined to tackle this but I could use some advice. Since it hasn't been turned on in 10 years, I'm reluctant to do so since the filter caps are probably not up to the task and I don't want to fry any other components. I assume it should be brought up on a variac for evaluation before going any further.

I see the tube compliment on these amps is peculiar and the prices for NOS replacements are expensive (but within my means).

Cosmetically, the amp has some grime and stains but the tolex and tweed are in pretty good shape. It has a 12" main speaker and the reverb speaker. It has the reverb footswitch. The front panel dials turn without trouble.

I can provide external and internal photos as desired although I just got this today and haven't opened it up or photographed anything yet.

I want to offer my buddy a fair price for the amp; recognizing the cost of the likely work it will take. I'm thinking a fair price would be the estimated selling price of a functional amp minus the cost of putting it in functional shape. My current SWAG is a selling price of $450 with at least $250 in repairs for testing, filter caps, a replacement tube or two, and perhaps some bucks for consulting with an amp tech.

I'll be glad for any advice on how to proceed. I'm certainly excited about this amp and would like to get it into playing shape for my own enjoyment and not for resale.

Thanks much
 

sailingshoes72

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Welcome aboard! There are a lot of fans of vintage tube amps here at LTG, and varying degrees of experience and expertise in repair and restoration. There are also a quite a few Guild amp schematics in members' collections. I personally let my amp tech handle any repairs, but others with more knowledge than me should be along shortly. I look forward to photos of your T-1 RVT.

Bill
 
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gilded

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Welcome,

Schematics are available for free on line someplace.

They're way cool amps. Absolutely Wonderful Vibrato-Trem', you won't hear many amps like it. No headroom. The power tubes, EL86s, are for European Radios; you get about 10-12 watts. They're quieter than they look. I gigged with mine once. Got buried in the rest of the band.

I think your pricing is okay, maybe a little better for you than your friend, but he may not care. I bought a clean one for a friend for $400 and he was ecstatic, so I guess it was worth more to him than that. One was snapped up instantly at a big guitar show a few years ago for $275.

I would think a clean one would be worth $500-600. That said, I've never tried to sell one recently. I do know that mine is not for sale!

Love to see some pics.
 

59Panhead

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You can bring it up on an auto-transformer, or some people call them a Variac. That's just the brand name of a popular type.

But, you can Google lamp limiter, and build yourself one of those at a reasonable price. I like them better, though I have both. You can watch the different wattage bulbs for problems as the amp comes up. I use 25, 40, 60, and 100 watt bulbs to reform old filter capacitors and watch for other issues. I typically let them 'cook' for 30 to 45 minutes on each bulb.

The 25 will almost always glow bright, but if there's a short, it will glow at its full brightness. By the time you get to the 60 watt bulb, you'll hear the amp start working. Who knows. The soak time while reformimg may even lessen the hum.

Jack
 

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Bill and gilded, thanks for the welcome and the schematics tip. I did find one for the amp but I can't tell if it is for version 1 or version 2 (which I have).

Jack, great tip about the lamp limiter. I don't have an auto-transformer and was going to borrow one. Question, do you know if discharging the filter capacitors via pin 1 of a 12AX7 tube and a 100k plate resistor to ground will work with this amp?

gilded, I appreciate the thoughts on the value of the amp. I want to be fair with my buddy so it is a win-win for both of us. Once I determine the overall condition of the amp and estimate the repair costs, I'll make sure he gets a fair price.

Wayne
 

Tubeblaster

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Guild Thunder I Reverb T1-RVT, version 2. Photos part 1.

Here are some photos I just took of the amp. The individual images are hopefully visible below but I've seen then inconsistently display. If you run into this issue, you can see them all via Google Photos at:

https://goo.gl/photos/J2bHosCZdSYBPx9m6

JBXbv6


oeDdwq


DJTxov


wwkwEh


SGKggC


1LYO1y


6aqLy3


Wayne
 
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Tubeblaster

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Guild Thunder I Reverb T1-RVT, version 2. Photos part 2.

Here are the rest of the photos of the amp. The individual images are hopefully visible below but I've seen then inconsistently display. If you run into this issue, you can see them all via Google Photos at:

https://goo.gl/photos/J2bHosCZdSYBPx9m6

UC83Sh


2i8dI6


BLACcQ


x36NWm


cJzr5a


W9bzQ8


6Ym8Nv


Wayne
 
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john_kidder

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You can bring it up on an auto-transformer, or some people call them a Variac. That's just the brand name of a popular type.

But, you can Google lamp limiter, and build yourself one of those at a reasonable price. I like them better, though I have both. You can watch the different wattage bulbs for problems as the amp comes up. I use 25, 40, 60, and 100 watt bulbs to reform old filter capacitors and watch for other issues. I typically let them 'cook' for 30 to 45 minutes on each bulb.

The 25 will almost always glow bright, but if there's a short, it will glow at its full brightness. By the time you get to the 60 watt bulb, you'll hear the amp start working. Who knows. The soak time while reformimg may even lessen the hum.

Jack
Jack - tell us more about this? I'm intrigued. I have a Thunderbird (big brother to the T1-RVT) that has an annoying habit of suddenly quitting after a half-hour or so of playing, but comes right back up when it's re-powered and then plays fine. Seems likely to be a heat issue to me, but I am no amp guy, and the local techs here in the desert are much better about tractors.

i do ecourage Tubeblaster to get the amp into shape. I love mine, do small single gigs with it often, and play through it at home frequently. Clean, warm, great reverb and term.
 
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I have a 64 Thunder 1 T-1 with just the Tremolo. Mine is the black version with the gold sparkle grill cloth. The amps are similar enough except mine has no reverb. The biggest changes that I've made were to the filter caps. Replaced all of the electrolytic filter caps with new ones from Antique Electronic Supply - they are a great parts vendor. Many choices for filter caps - in my case just used basic IC brand but Sprague Atom are highly recommended as are F&T. I don't have the schematic in front of me but there are 3 total filter caps to change. I also changed a couple of resistors in the power section and put on a grounded power cord. Mine had the 2 prong. The tremolo did not work and I determined that it was because the switch was fused in the "off" position. A radio shack switch fit the slot with a little bit of modification and was pretty easy to wire in. Tremolo works great now. Very unique sound. I did not change any caps or resistors in the tone stack at all. The amp tone is absolutely perfect and designed to sound "full range" like a hi-fi stereo. I really prefer this sound so no changes to the tone stack are recommended unless you detect something out of spec. Mine was purchased on ebay and arrived with the original CTS speaker completely destroyed. The cone was ripped apart. Because the seller had listed it as fully functional, I was able to get a significant credit and actually only paid around $150 for the amp. For the speaker, there are many choices if you choose to replace it. Many times when restoring vintage amps I end up changing the speaker. It's been my experience that many of the old CTS speakers don't hold up today so it makes sense to swap them out if you are going to use the amp to perform or rehearse with. I've tried everything and realize that Jensen (made in Italy now) are the best. The specific one I recommend for this amp is the Jensen Jet Falcon 8 ohm. It's a 10 inch speaker. Will sound great....Not sure if your amp has the separate reverb speaker - if so I'd recommend the 8 inch Jensen MOD for that one. Although I did a lot of work on this amp myself, in the end I did bring it to an excellent tech (Cove Electronics in Newport RI) who tightened it up further by finding another out of spec resistor and changing a bad tube that I missed. It's well worth the effort and one of my favorite amps. It's a lot louder with a new speaker and after restoration and I've used it on-stage for events at my kid's school in the Gym and had no problem being heard...of course the drummer was a kid and we were playing "Candyman" - the sammy davis JR version, but that's a different story...
 

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Re the electrolytics: My 3 friends who build amps for fun would generally choose the F&T caps.
 

59Panhead

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Jack - tell us more about this? I'm intrigued. I have a Thunderbird (big brother to the T1-RVT) that has an annoying habit of suddenly quitting after a half-hour or so of playing, but comes right back up when it's re-powered and then plays fine. Seems likely to be a heat issue to me, but I am no amp guy, and the local techs here in the desert are much better about tractors.
My first suspicion is the power transformer, but it could very well be tubes. If you have a tube set that you can swap out to confirm, I'd start there. If that is not the fix, I'd have the chassis out on the bench, connected to a speaker, and a voltmeter connected to the secondary of the PT. Then, I'd try to duplicate the problem, all the while watching the voltmeter. If it is the PT, Mercury Magnetics will more than likely have a direct replacement, with the same footprint. Hammond will have a replacement, probably cheaper, but may not have the same footprint. If you feel safe doing this, I'd give both a try.

Jack
 

59Panhead

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Jack, great tip about the lamp limiter. I don't have an auto-transformer and was going to borrow one. Question, do you know if discharging the filter capacitors via pin 1 of a 12AX7 tube and a 100k plate resistor to ground will work with this amp?
I prefer to discharge all caps right at the power supply, and not at the tubes.

Jack
 

59Panhead

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Jack - tell us more about this? I'm intrigued. I have a Thunderbird (big brother to the T1-RVT) that has an annoying habit of suddenly quitting after a half-hour or so of playing, but comes right back up when it's re-powered and then plays fine. Seems likely to be a heat issue to me, but I am no amp guy, and the local techs here in the desert are much better about tractors.
I have a generous supply of tubes on hand, so I tube-swap, first. Then, I lay the chassis out on the bench, connect a speaker, connect a voltmeter to the secondary of the power transformer. In you case, play it until you can duplicate the problem, watching the voltmeter. If you voltage drops when you lose the amp, you may have some windings breaking down in the PT. Mercury Magnetics will more than likely have a direct replacement, with the correct footprint for mounting. Hammond will have a replacement, but the footprint may not match.

If you have the means, try those and see what happens.

Jack
 

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Jack... what is the theory behind bringing up a vintage amp on an auto-transformer? I have several amps that have been in climate-controlled storage for about 10 years. During that time they have not been powered up or played. And what does "reform old filter capacitors" mean? (I understand what power supply capacitors are and what they do.) These days I mostly play a silverface Vibro-Champ in the living room, but recently I have been thinking about getting one of my other amps out of storage. I do have a friend who has a Variac.

Thanks, Bill

Amps in storage:
1953 Newcomb G-12 (basically the same AT&T/Western Electric circuit as a Deluxe 5C3)
1966 Fender Princeton (non-Reverb)
1967 Ampeg Gemini I (7591A power tubes)

Also, all three amps had been recently been serviced, and were in excellent working condition before they went into storage.
 
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59Panhead

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Jack... what is the theory behind bringing up a vintage amp on an auto-transformer? I have several amps that have been in climate-controlled storage for about 10 years. During that time they have not been powered up or played. And what does "reform old filter capacitors" mean? (I understand what power supply capacitors are and what they do.) These days I mostly play a silverface Vibro-Champ in the living room, but recently I have been thinking about getting one of my other amps out of storage. I do have a friend who has a Variac.

Thanks, Bill

Amps in storage:
1953 Newcomb G-12 (basically the same AT&T/Western Electric circuit as a Deluxe 5C3)
1966 Fender Princeton (non-Reverb)
1967 Ampeg Gemini I (7591A power tubes)

Also, all three amps had been recently been serviced, and were in excellent working condition before they went into storage.

Bill -

A quick search of the Internet will give a better description of reforming caps, than I can. But in a nutshell, caps (particularly, electrolytics) don't do well sitting on the shelf. They must be charged and discharged to stay 'healthy'. If not used for long periods, amps should be powered up periodically. That being said, I have a lot of amps just sitting. But, I also have a number of these lamp limiters made up and close by. None of them go straight to full wall voltage, until they get a bit of soak time.

Even still, this reforming does not always work on old caps. You can do what would seem to be a successful reforming, only to have the end blow out of a filter cap. But in your case, if they were serviced before storing, you should not have this issue. Still, to take proper care of you amps, ease them back into service. The initial expense of a lamp limiter is low, and well worth the build. Like I said about the auto-transformer, you can't see how the amps are coming up, other than the voltage reading. Light bulbs tell a good story. The 40 watt bulb will change in intensity, as the caps are charging and the tubes start conducting. The 60 watt will do similar, but stay dimmer. The 100 watt will probably stay fairly dim, after the previous bulbs have performed the initial conditioning. Don't depend entirely on the 25 watt intensity, unless it glows very brightly, and gets hot quickly. Something's wrong. If the 40 watt does the same, don't even bother with the 60 or 100. You may pop a fuse.

You are preventing potential damage to other components that you can see. I don't have a good picture of my limiters, but here's one being used with a 25 watt bulb, on new caps. I treat them the same way:



Jack
 

sailingshoes72

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Jack... thank you for taking the time to respond to my questions. It is vey helpful! I was planning on pulling the amps out of storage, plugging them into the wall, letting the tubes warm up and then playing one of my guitars. Now, I'll bring them up slowly on a current limiter and monitor the amps as the filter caps and plates approach full voltage. And, I will research "reforming capacitors". This has been a very timely Thread for me! Also, that is a very cool Ampeg Portoflex on your bench.

Wayne... I was unable to view your photos. It may be because they need to be screened by a moderator, as you are a new member. But, I was also unable to view them on the link to photos/google. My first thought is always that my software is out of date... but I thought I would mention it.

Bill
 

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I have a 64 Thunder 1 T-1 with just the Tremolo. Mine is the black version with the gold sparkle grill cloth. The amps are similar enough except mine has no reverb. The biggest changes that I've made were to the filter caps. Replaced all of the electrolytic filter caps with new ones from Antique Electronic Supply - they are a great parts vendor. Many choices for filter caps - in my case just used basic IC brand but Sprague Atom are highly recommended as are F&T. I don't have the schematic in front of me but there are 3 total filter caps to change. I also changed a couple of resistors in the power section and put on a grounded power cord. Mine had the 2 prong. The tremolo did not work and I determined that it was because the switch was fused in the "off" position. A radio shack switch fit the slot with a little bit of modification and was pretty easy to wire in. Tremolo works great now. Very unique sound. I did not change any caps or resistors in the tone stack at all. The amp tone is absolutely perfect and designed to sound "full range" like a hi-fi stereo. I really prefer this sound so no changes to the tone stack are recommended unless you detect something out of spec. Mine was purchased on ebay and arrived with the original CTS speaker completely destroyed. The cone was ripped apart. Because the seller had listed it as fully functional, I was able to get a significant credit and actually only paid around $150 for the amp. For the speaker, there are many choices if you choose to replace it. Many times when restoring vintage amps I end up changing the speaker. It's been my experience that many of the old CTS speakers don't hold up today so it makes sense to swap them out if you are going to use the amp to perform or rehearse with. I've tried everything and realize that Jensen (made in Italy now) are the best. The specific one I recommend for this amp is the Jensen Jet Falcon 8 ohm. It's a 10 inch speaker. Will sound great....Not sure if your amp has the separate reverb speaker - if so I'd recommend the 8 inch Jensen MOD for that one. Although I did a lot of work on this amp myself, in the end I did bring it to an excellent tech (Cove Electronics in Newport RI) who tightened it up further by finding another out of spec resistor and changing a bad tube that I missed. It's well worth the effort and one of my favorite amps. It's a lot louder with a new speaker and after restoration and I've used it on-stage for events at my kid's school in the Gym and had no problem being heard...of course the drummer was a kid and we were playing "Candyman" - the sammy davis JR version, but that's a different story...

Thanks so much for detailing your rebuild and the speaker recommendations. The main speaker in this amp is an Oxford 12 and the reverb speaker is a CTS.
 

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My first suspicion is the power transformer, but it could very well be tubes. If you have a tube set that you can swap out to confirm, I'd start there. If that is not the fix, I'd have the chassis out on the bench, connected to a speaker, and a voltmeter connected to the secondary of the PT. Then, I'd try to duplicate the problem, all the while watching the voltmeter. If it is the PT, Mercury Magnetics will more than likely have a direct replacement, with the same footprint. Hammond will have a replacement, probably cheaper, but may not have the same footprint. If you feel safe doing this, I'd give both a try.

Jack

I've used Mercury Magnetics iron in my Fender Deluxe Reverb rebuild and was quite happy with them. They didn't initially have a power transformer to fit the Fender Deluxe Reverb Reissue chassis I was using but they built one for me. I checked, and they list an output and reverb transformer available for the Guild Thunder Reverb but it looks like they'd have to make a power transformer, at least according to this page on their website:

http://www.mercurymagnetics.com/pages/catalog/manufacturers/MM_misc.htm
 

Tubeblaster

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. . .

Wayne... I was unable to view your photos. It may be because they need to be screened by a moderator, as you are a new member. But, I was also unable to view them on the link to photos/google. My first thought is always that my software is out of date... but I thought I would mention it.

Bill

Bill, thanks for pointing out the photo problem. I found it to be intermittent. I subsequently put all the photos in a Google Photos album and provided a link at the top of my posts with the photos. You should be able to use that to see them all. If not, please let me know and I'll try something else.

Wayne
 
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