Power transformer replacement for Thunderbird

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Hello all, new member but long time stalker. My go to amp, a beast of a 2x12 Thunderbird has ceased functioning and I'm calling out for help. I have never been able to determine what version Thunderbird I have as there is some contradictory info on various sites. It appears to be 1969 or 1970 version ll however the photos I've found are not dead on. The power transformer is no longer putting out any voltage when applying 120 to primary so I'm assuming it is kaput. My Thunderbird is the tall 2x12 Concertos, non-master volume, 2x7591, solid state rectification, point to point wired separate pre-amp and power amp. If anyone knows what modern power transformer will work or the voltages that need to be provided by the transformer I would be in your debt. The only schematics I've found for Thunderbirds either featured tube rectification or 6l6's so no help.
Thanks in advance.
johnny99
 

The Guilds of Grot

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Hey johnny-99, welcome to the board. I am of no help with your question but we do have some "amp" guys here. Default will probably answer when he is on his lunch break!
 

Default

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I would look at the Maverick schematic for compatibility. If I get my act together I'll see what the numbers are on my mav and my T-bird.
 

fronobulax

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Welcome.

@AcornHouse may have something to contribute.

I appreciate a first post that asks a question and tells what you think you already know.
 

jp

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Hi johnny and welcome to the forum!

Here's a past thread that may help you identify which generation your Thunderbird is from.


Forum member matsickma is also very knowledgeable about Guild amps and may chime in. Unfortunately, our dear amp pro capnjuan from that thread is no longer with us (but not forgotten).

Also, if you ultimately can't find the answer here, I'm sure a call to Mercury Magnetics could help you nail it down.
 

matsickma

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Sounds like you have a "missing link" Thunderbird amp or one that was modified.
Look closely at the power amp section attached to the side of the speaker cab area. Their may be a label indicating a name for the power amp section. Also note if the cable between the "head" and power amp section looks modified.

I think you may have the 3rd version of the Thunderbird amp but the power section is from a Thunderstar amp. The Thunderstar guitar amp used 7591A power tubes and the stock 3rd version Thunderbird used 6L6 output tubes as did the Superstar amp.

I thought the connector for the 7591A Thunderstar power amp section used a different connection from the 3rd Thunderbird and Superstar power amp sections. Also I don't recall the rectifier being solid-state.

I will have to see if I can get at those amps to inspect the connection.

So for now look at the schematic for the Thunderstar guitar amp for info on the power supply and power transformer.

M
forla
 

AcornHouse

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Sounds like you have a "missing link" Thunderbird amp or one that was modified.
Look closely at the power amp section attached to the side of the speaker cab area. Their may be a label indicating a name for the power amp section. Also note if the cable between the "head" and power amp section looks modified.

I think you may have the 3rd version of the Thunderbird amp but the power section is from a Thunderstar amp. The Thunderstar guitar amp used 7591A power tubes and the stock 3rd version Thunderbird used 6L6 output tubes as did the Superstar amp.

I thought the connector for the 7591A Thunderstar power amp section used a different connection from the 3rd Thunderbird and Superstar power amp sections. Also I don't recall the rectifier being solid-state.

I will have to see if I can get at those amps to inspect the connection.

So for now look at the schematic for the Thunderstar guitar amp for info on the power supply and power transformer.

M
forla
And that would be here.
https://www.gad.net/Blog/knowledge-base/s-thunderstar-amp/
 

Nuuska

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Hello Johnny-99

Greetings from cold weather Finland
Welcome to The Warm heart of Internet 🥰
 

Default

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I don't know about that amp being a missing link, I've seen them before with the split chassis. The horizontal ones all seem to have the single chassis and the vertical ones seem to have the split chassis. I actually think that the 2x6l6 were just using parts toward the end. No proof, just a feeling. The the B+ may be a voltage doubling circuit on those. Can you post a pic of the amp with the back panel off?
 

matsickma

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Just looking at the Instruction manual for the Thunderstar abd Thunderbird amp in GAD's attached posting. The instructions indicate that the Thunderbird amp has a Master volume control while the Thunderstar doesn't. It would seem that Guild didn't roll out the new preamp stage of the Thunderstar amp to the Thunderbird and the pending Superstar amp. The last version of the Thunderbird and the Superbird did have a advertising flyer indicating 6L6 tubes being used. So it may be another example of Guild not waisting any parts and using up inventory.

M
 
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Thank you to all, I appreciate the support. I will post some photos when I get home although both chassis are out of the cab. I bought the amp about twelve years ago and have always gone back to it for it's tone, obviously not for it's portability. Other then replacing electrolytic caps and a few resistors it has been flawless until no standby light last week, aka, no heater voltage....The amp overall is in amazing shape and there are no signs of prior mods or repairs. This is better then the best blackface deluxe reverb tone I've ever heard but when dimed the distortion is different, a bit less compressed, I just love it. I contacted Mercury but no luck, still waiting on a response from Hammond. Worse case I can try a few different pt's that can provide sufficient high voltage, heater and bias and then measure and compare to schematics, more work but she'll sing again.
My best to all,
johnny in jersey
 

matsickma

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I personally love the tone out of Guild amps with 7591A tubes.
Initial Thunderbird amp, 2nd version Thunderbird amp, Thunderstar and Maverick were the ones that I was familiar with. I would rate the 2nd version Thunderbird as my favorite but the 1st version and Maverick were very close behind. The Thunderstar was no slouch either but I think the speaker mounting affected the tone in a way that was less to my preference. Someday I will do a little modification to alter the Thunderstar speaker surround port. I will close it up and re-evaluate with and without the back open.

M
 
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Just got an email from Mercury with a drawing of the only thunderbird pt they offer, no idea for which version however the voltages listed are 329-0-329, 6.3 and 13. In looking at all of the Guild 7591 power amps I can find schematic's on I believe I see 15 volts on bias supply and 360-0-360 although the print blurs when enlarged so I'm not sure. Anyone know the correct bias supply. I can get close with the power transformers I have here except on the bias voltage, they are all 50 volts.
A side note, a local radio station her at the jersey shore is running a greatest rock lead guitarist of all time contest based on listener votes, the quarter finals have Slash versus Jimmy Page and Hendrix vs Van Halen, Van Halen is currently leading Jimi by 10 points, SRV, Clapton, Beck and Mayer have all perished as I fear Jimi will too, a dark day indeed......

My best,
Johnny in jersey
 

Nuuska

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Negative bias voltage is derived from anode coil - before main rectifier is a diode and then some RC to filter it. Current on that circuit is next to zilch.
 

matsickma

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I feel your pain!
Eddie VH was a natural guitar player and his style set the standard for the 80's which I enjoyed greatly and I didn't associate his playing as that of the "hair band" genre inspite of Diamond Dave's antics.

Jimi was, as Jack Bruce said "a force of nature"! His musical output in such a short four years of time was equal to or exceeded the Beatles and established a synergy between his hands, guitar, amp, songwriting, technique and musicality that still amazes guitarist to this day.

Nothing against EVH as I listen to his music often but James Marshall Hendrix's is the Blues/Rock master to this day and for decades to come! (IMHO)
M
 
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