Guild Thunderstar Bass head

mellowgerman

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Casually in the market for a Guild Thunderstar Bass amp head. I used to own a 1968 blue-face model and miss that tone quite a bit. Not in a big hurry, but actively seeking.
A big factor for me, also why I'm willing to take my time with this, is that I would like to find one that has recently been serviced and gone through.
Please let me know if you know of one that's up for grabs. Thanks!

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mellowgerman

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There is a nice Thunderbass on Reverb (at Maindrag Music in Brooklyn), which is intriguing, but if I will probably try to find a Thunderstar first, since I know that has the exact tone I remember and am thinking of
 

mellowgerman

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Well, the search has ended. Yesterday I added a Thunderbass head to the collection. It's all original, down to the tubes and two-prong plug. Sounds fantastic though and the pots aren't even that scratchy! In any case, I will seek out a good amp tech in the area to go through it and replace whatever needs replacing.
 
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AcornHouse

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Well, the search has ended. Yesterday I added a Thunderbass head to the collection. It's all original, down to the tubes and two-prong plug. Sounds fantastic though and the pots aren't even scratchy! In any case, I will seek out a good amp tech in the area to go through it and replace whatever needs replacing.
Congrats! I’m working on resurrecting my 2nd one.
Is yours 6L6 or 8417 power tubed? (I think there is even a 6550 version.)
 

mellowgerman

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Congrats! I’m working on resurrecting my 2nd one.
Is yours 6L6 or 8417 power tubed? (I think there is even a 6550 version.)

I have two RCA 8417's in the power section. I was told they are probably still the originals. From what I understand, they're not easy to acquire these days. Would like to have the amp converted to 6L6 for this reason, but I'm not sure how big of a project that would be... it's the power-supply that needs to be modified to the 6L6 specs, no?
 

mellowgerman

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here's the rear end (back panel is missing, but that gives it more air to breathe I suppose)

kF4GqII.jpg


here it is with my baby

RNNFlOs.jpg


and here's the full line-up!

cZUpKzZ.jpg
 

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I have two RCA 8417's in the power section. I was told they are probably still the originals. From what I understand, they're not easy to acquire these days. Would like to have the amp converted to 6L6 for this reason, but I'm not sure how big of a project that would be... it's the power-supply that needs to be modified to the 6L6 specs, no?

Depending on which version of the T-bass you have, the voltage on the plates could be 400 volts(for the 50 watt version) or 540 volts (for the 100 watt version). The big issue is the bias circuit won't put out the -35 volts you need to bias a 6L6 - it only puts out about -20 volts, which is all the 8417 needs. You would probably have to tap off the 120 wall voltage via a rectifier to get the proper voltage to the bias.
 

mellowgerman

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Here are a few more shots... my phone camera is not the best, but I was hoping that maybe these might help in figuring out what year it might be from. I know they are not easily traceable. It looks to me like most of the pots I can see are dated to 1967 if I'm interpreting the code correctly.
Pretty clean for a vintage Florida amp right? I feel like a lot of times they have more rust from the humidity

Nf66ggJ.jpg

LRc2qFX.jpg

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mavuser

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good score, just run the original tubes and don't worry about it.
 

Nuuska

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Hello

If there is schematics for that amp - I have a friend with about 1500 tubes and plenty of know-how - we will help.
 

mellowgerman

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Yeah I may just stick with 8417's. Even if they are pricey, I am no longer a touring bassist and will rarely have the opportunity to break out the Thunderbass and really open it up to jam with others, so I imagine that if I have a tech look it over now, replace any caps that need it, swap the power cable, etc. she should be good to go for quite a long time. Then if the once-in-a-blue-moon $150-200 tube swap is necessary, it will be well worth the pleasure of enjoying the amp as its creators intended it.

Also, I did manage to acquire a schematic and rather lengthy instructional manual for the whole Thunderbass line from a gentleman on the talkbass forum... it seems to cover a lot of the different variations of the amp. If anybody would like a copy, it's a pdf and I'd be happy to share

Thanks for all the input and help, guys!
 
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AcornHouse

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Yeah I may just stick with 8417's. Even if they are pricey, I am no longer a touring bassist and will rarely have the opportunity to break out the Thunderbass and really open it up to jam with others, so I imagine that if I have a tech look it over now, replace any caps that need it, swap the power cable, etc. she should be good to go for quite a long time. Then if the once-in-a-blue-moon $150-200 tube swap is necessary, it will be well worth the pleasure of enjoying the amp as its creators intended it.

Also, I did manage to acquire a schematic and rather lengthy instructional manual for the whole Thunderbass line from a gentleman on the talkbass forum... it seems to cover a lot of the different variations of the amp. If anybody would like a copy, it's a pdf and I'd be happy to share

Thanks for all the input and help, guys!
I’ve used my 8417 TBass in half a dozen concerts or so without worrying about the tubes. Just get those electrolytics changed.

I think I have all of the various schematics for the variants, but I wouldn’t mind getting a copy of that .pdf to see if it has any thing new to me.
 

AcornHouse

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Oh, and can you post the codes stamped in the transformers for me? I’m still trying to determine if my second TBass is an 8417 or 6L6, it’s been mucked up so much.
 

mellowgerman

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I’ve used my 8417 TBass in half a dozen concerts or so without worrying about the tubes. Just get those electrolytics changed.

I think I have all of the various schematics for the variants, but I wouldn’t mind getting a copy of that .pdf to see if it has any thing new to me.

Cool beans. If you want to private message me your email address I'll zap it on over to ya. Also, will post the transformer code when I get home. A friend of mine who had a peak at it said it dated to 1968, so that at least narrows down the possible age of the amp a bit. Also, would love to have a schematic specific to the amp that I have, but I guess it might take a minute before I really know exactly what year/version I have
 

AcornHouse

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Transformer codes are:

007017
606801

Hope that helps!
Interesting. The top model number is the same as my supposed 6L6 one, but yours is manufactured by Woodward-Schumacher, mine is Todd Electrical.

That might be why it’s burnt.
 

Nuuska

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Interesting. The top model number is the same as my supposed 6L6 one, but yours is manufactured by Woodward-Schumacher, mine is Todd Electrical.

That might be why it’s burnt.


Hello

if your amp was designed for 6L6 and 8417 was used - I can see a reason for burnt mains transformer. Two 6L6 require 1,8 amps heater current - two 8417 soak 3,2A - replace the fuse with bigger and wait for the smoke...

Other than that I see the conversion is easy. Anode voltage is lower than max - no harm there. Negative bias voltage can easily be reduced to suitable level.
 
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