Thunderstar (Lead?) Combo......

59Panhead

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I'm planning my repairs on this amp. The spring tank had one broken spring, the input is completely open (no resistance), and the Reverb transformer is cooked. I pulled the 6GW8 tube and brought the amp up on the lamp limiter. After doing this, I fired it up and it sounds good. The Tremolo is weak, but I can chase that issue later. I want to repair the Reverb circuit first.

I can find no specs on the '4G' spring tank. And, the only specs that I can find on the transformer is one matching my numbers (007013 9264761) from Mercury Magnetics. They emailed me and told me the Primary impedance was 5K ohms, and the Secondary was 8 ohms. I have been trying to find more. Just no luck.

Can anyone confirm these impedances from some original literature? I have the Accutronics spring tank data sheet, but it has no info on these tanks. Thanks for any help. Have a good one.

Jack
 

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Here's a chart that you probably already found. It's got to be an 8 ohm pan, that's the only thing that makes sense with the 6gw8. Not sure what the output impedance is, but mavuser subbed in a standard Fender pan and it worked fine.


reverbtank3.svg
 

59Panhead

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Yes, I have that chart on hand. But, thanks for posting. Always good to have it in front when making reference to spring tanks.

Makes me wonder why the transformer cooked, and the tank input was open. I checked the tube on my B&K 707, and it seems to be fine. Not super strong. But, should work ok. I compared it to another that I have, and they both seem to be the same. So, I can compare both of them.

I have a MOD 4ABC3C1B that I'll use as my test tank, when I have the circuit repaired. I'm beginning to wonder if the letter in the '4G' designates the mounting position. The Guild and Ampeg both use this labeling for their tanks. And typically, their tanks are transformer driven. Meaning, the 60's and older amps, which are really the only ones that I'm familiar. The Fliptops have their tanks mounted horizontal (4F). This amp has it vertical.

Jack
 

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Guild's reverb is based off the Guild reverb converter amp, which is stolen from the Gibson RVT-1, fwiw. The scheme is at Prowess Amp's website.
 
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mavuser

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I can add to this thread, although I am not an amp tech...based on the info I have gathered over the years. Much of what has been posted seems conflicting with my understandings to this point. Pan head there is a chance your transformer is not original and/or wrong. There is a chance your reverb is not even driven by a transformer (although I believe it is at this moment). The pan I replaced was in a maverick , not a Thunderstar. I don't think at this moment that makes a difference but it might. The original maverick pan was a "Gibbs special product reverberation unit". It had 2 springs. I never heard the amp with the reverb working with the original pan in it. My Thunderstar is original and the reverb sounds different than the mavs, but again the Mav pan is a non original.

I have a lot more concrete info to add to this, and specific fact checking on what has been posted above. but can't do it until later. I believe some of the info above might be incorrect.
 

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According to the schematic, it is. When I get home, I'll see about pulling the mav out of storage. I don't think it's marked, but I'll check again.
 

59Panhead

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I can add to this thread, although I am not an amp tech...based on the info I have gathered over the years. Much of what has been posted seems conflicting with my understandings to this point. Pan head there is a chance your transformer is not original and/or wrong. There is a chance your reverb is not even driven by a transformer (although I believe it is at this moment). The pan I replaced was in a maverick , not a Thunderstar. I don't think at this moment that makes a difference but it might. The original maverick pan was a "Gibbs special product reverberation unit". It had 2 springs. I never heard the amp with the reverb working with the original pan in it. My Thunderstar is original and the reverb sounds different than the mavs, but again the Mav pan is a non original.

I have a lot more concrete info to add to this, and specific fact checking on what has been posted above. but can't do it until later. I believe some of the info above might be incorrect.

It is an original, unmolested amp. Some of the tubes are not original, though they are all old. This amp was very active at some point.

No signs of any of the soldering being touched. And, the Reverb OT is most definitely original to the amp. I believe the Reverb has been non-working for some time. I also believe the broken spring came from shipping. Spring tank springs must be padded before shipping, or this happens. I can't think of the number of times that I've replaced spring tanks, just because they were damaged in shipping.

But, I would like to hear more. Please post when you are able. Have a good one.

Jack
 

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I'm at work, so I'm hobbled with the phone. The Guild Reverb converter amp schematic is bundled with the 98 RVT schematic at Prowess. Should be interesting to compare the two.
 

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yes the reverb in the Guild Thunderstar is transformer driven. but i'd still like to address these 2 generalized statements...

Guild and Ampeg both use this labeling for their tanks. And typically, their tanks are transformer driven. Meaning, the 60's and older amps, which are really the only ones that I'm familiar.

Guild's reverb is based off the Guild reverb converter amp, which is stolen from the Gibson RVT-1, fwiw.

...with some prior posts from the Capt'n (RIP):

Hi Eric; all reverb cans look alike but there are several things that make them different; orientation of in/out jacks, # and length of springs .... but the most important characteristic is the input / output impedance ... and you can't tell that just by looking. In the pic below, the little yellow thing in the blue circle is a transducer ... there's one at the input and one at the output .... they have to match the impedance of the circuit or else the can won't work correctly.

-sorry no picture-

Fender, Gibson, and many others used a small transformer in between the reverb 'drive' tube and the can. Ampeg, Guild, and others used a capacitor to connect or couple the drive tube to the can. The output impedance of a Fender/Gibson transformer is 8 ohms. Any can to be used that is driven by a transformer has to have 8 ohm impedance. If the can is coupled by a capacitor, the input impedance of can (the transducer) is usually about 2.5K ohms.

This is not a matter of whether a 8 ohm input can or a 2.5K input can sounds better. One will not work in a circuit designed for the other. Before betting that it's the tube, you ought to call you tech and ask him either what the can's input impedance is or what kind of an amp was it made for.

captn's above post says ampeg and guild used capacitors, so are you saying the maverick is an exception to most guilds and has a transformer like a fender?


***

Hi Eric; my apologies for contributing to the confusion. Guild's earliest reverb amp, the 98RT, used an Ampeg circuit that coupled the can with a capacitor. Guild later used the 12" speaker in their Thunder 1 RVTs and Thunderbirds to couple the reverb can. In the later 60s/early 70s they adopted the more conventional transformer-coupled design. The Maverick uses a transformer...unless the 6GW8 reverb drive/recovery tube has been over-stressed, the several resistors and capacitors that make up the reverb circuit are likely to fail sooner than the tube will.

***

Makes me wonder why the transformer cooked,

again, i refer you to this (altough there may be more to it):

unless the 6GW8 reverb drive/recovery tube has been over-stressed, the several resistors and capacitors that make up the reverb circuit are likely to fail sooner than the tube will.

now onto your transformer code:

And, the only specs that I can find on the transformer is one matching my numbers (007013 9264761) from Mercury Magnetics. They emailed me and told me the Primary impedance was 5K ohms, and the Secondary was 8 ohms.

here's where it gets a little merky.

Both my Maverick and Thunderstar have the same reverb circut design (transformer driven). both of them have 3 transformers each. all six transformers have Schumacher codes (the same transformers used in Fender blackface and silverface amps). I understand the date codes on mine but not value codes. I think I know which of the 3 transformers is the reverb transformer, but to be honest im not positive. but I will list them all here, and could post pictures if you need-


Thunderstar- 1969/1970

Transformer "A" (Identical codes to the Maverick)
007006
606-8-13 (
Schumacher 13th week 1968)

Transformer "B" (smaller reverb? tranny)
007023
606942 (Schumacher 42nd week 1969)

Transformer "C"
007005
606814 (Schumacher 14th week 1968)

Maverick-1970/1971

Transformer "A" (Identical codes to the Thunderstar)
007006
606-8-13 (
Schumacher 13th week 1968)

Transformer "B" (smaller reverb? tranny)
007023
606026 (Schumacher 26th week 1970)

Transformer "C"
007025
606-0-31 (Schumacher 31st week 1970)

So as you can see, none of my transformers have the same codes as yours. I'm not sure what the top numbers ("007xxx") are for but its probably some sort of value (like a tone pot on a guitar?)

the Reverb OT is most definitely original to the amp.

that is certainly possible, but you can understand why I would question it as being -definite- based on what I know (which really is not much at all, just gathering info...)

It is an original, unmolested amp. Some of the tubes are not original, though they are all old. This amp was very active at some point.

that statement contradicts itself just a little. just sayin. (sounds like a nice TStar though!)

I hope something here helps you a little. if you need pictures I can post them but the codes above tell the tale. If anything please post a picture of your Mercury Tranny 007013 9264761...thanks!



 

59Panhead

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I still consider it unmolested, if you are inferring the contradiction to be non-original tubes. I don't expect any old amp to have original tubes. This one is not beat up, though it has dings. By unmolested, I'm stating that there are no signs of any component changes inside the chassis', or any other mods. To me, tube changes are expected. Like tires and oil changes.

And over the years, I've come to expect spring tank replacements as a norm for improperly shipped amps. In this case, the Reverb tranny, as well. Just part of the restoration process. Make it as much as like it was. The proper tank will be some pricey. Vertical mount tanks have to be special ordered. A tank made for horizontal use will work just as well. I'll do that, until the proper tank can be had.

Jack
 
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