Thunderbird 1x12 + 1x8 combo

I'm intrigued by this amp but know very little. I've read that the reverb drives the 8" speaker. True (or did this vary from one model to the next)? I've not been able to find much here or on TGP in the way a basic review of features and tones. Anyone able to fill in some of these blanks?

Hi Leon: the Thunder 1 RVT was produced in two variations but with only cabinet and cosmetic differences; the circuit wasn't changed including speaker-driven reverb using an R/C in series. I just emailed you the schematics I have. Note that the reverb on/off switch is mis-labeled; when off, the line signal is tapped at the final gain stage, fed to the triode half of the reverb amp's 6BM8, and the reverb amp is used to reinforce the dry signal.

I also have the no-verb / tremolo variant T1; sold with 10" or 12" speakers if you want them. Miscellaneous pics Here ... and a tale of T1 RVT woe Here. Long-running thread about the T1s Here. The T1 RVT is 2X12AX7, 2X6GW8 and a 6CA4 rectifier. The stand-alone reverb amp is 12AX7 and 6BM8. The amp is fixed bias but with no means of adjustment; the tremolo manipulates grid bias. At least this amp and the Version 1 Thunderbird were made of particle board adding a degree of shipping risk. Later Thunderbirds used finger-jointed plywood; other than the two cosmetic variants, there weren't any later single, or twin-speaker, RVTs. John

Hey John, thanks a bunch for the info. Great stuff. I have found these thread in my research, and they're helpful from a technical standpoint and just historically interesting. Thanks for the schematic too; I imagine I'll get a little feel for some performance characteristics once I dig into the schematic and get familiar with the design a bit (cathode vs fixed, feedback loops, etc.) But having never played one (at least that I can recall)....

What I still don't have a good feel for is what do the amps sound like? E.g., were they real "clean machines", intended for accordion players? Were they tweedy, easily overdriven low-headrooom grind-boxes? Kinda "hard sounding" and black-faced-like? Ampeg-like? Did they tend to be really bright (like some Gibson Crestlines)? Really scooped? Really mid-rangey like Ampegs with 6S?7s? Do they get as loud as Reverb-o-Rockets or Geminis? Of course I know it'll vary from model to model...but I guess I'm most interested in the Thunderbirds.

Hi Leon; I should have known you'd have done your homework ... :wink: The amps shine principally with jazz and swing and do least well with roots/vintage R&R/blues; on the clean-to-dirty dial, they point towards clean. With twin 6GW8s, they are a little under-powered at 12 watts and very few other amp makers based their designs on the 6GW8.

They have .15uf PI-to-output coupling caps (7 times the more conventional .02uf usually found there) that filter out high frequency fizz, sizzle, and grit which ... to some ears, is a necessary ingredient of good vintage tone. The amps were designed to support Guild's line of wide-body jazzer guitars and at least have something in the catalog and on the show-room floor that somebody back in the day considering a Starfire could plug into and demo the SF with. Since there are hundreds more vintage Starfires than there are T1 RVTs, apparently a lot of SF buyers didn't buy them ... and neither did anyone else. From there, you can draw your own conclusions.

The Thunderbirds are another story; also used speaker-coupled reverb. A very clean model Here on eBay. Never worked on or played through one; several owners here, they have good things to say about them.

Thanks for another thing I hadn't noticed, capn! The ugly black thunder I rvt I'm trying to get rid of is older and appears to be particle board cab...the pretty blonde newer one is plywood! I was used to the particle board, but obviously plywood is much preferred. I didn't now they changed cab construction.

Hi Count: matsickma pointed out last year that the T1 10" and 12" cabs were mostly, or all, plywood but the T1 RVTs were particle board ... I thought they were all particle board. The early Thunderbirds are particle board but not sure about the later ones. J

I own a '65 black Thunder 1 with a 12" speaker. These I'm sure were Guild's answer to the Fender Princeton and having owned both I can say that the Guild as a nicer compression, whereas the Fender has more bottom end and "spank". If you took a Princeton and give it a more Vox like tone stack you'd get the idea. These are great amps for Fender Strats and Teles, they compress so nice (due to the EZ81 rectifier, just as a vintage Vox uses) with them and even if they were intended for jazz, they make great amps for that signature 60's rock and roll tone I'd say. I do a lot of Chet Atkins style playing and the note definition and string dynamics are much better than a Fender to my ears, nice for me others like the Fender "mojo" YMMV. To sum up they have a very nice clean "chime" to them. The stock speaker is a CTS which are not that good, and what people most form their opinions on when they describe this amp's tone. But when you swap out the speaker for a Celestion or good Jensen they turn into one of the best known secrets. The only down side is that the power tubes , 6GW8s are no longer made but NOS and good tested ones are avail (eBay, etc). So you just need to stock up on those.

Thanks very much for the description.

I'm not very technically knowledgeable so bear with me. I'm not familiar with EZ81s. Are these octal tubes? Does the compression result because the EZ81 is a bit small and is not providing "enough" juice to the power tubes for them to "keep up"? I believe I've experienced this sort of thing before with an old Sears 1482 (which was capable of really sounding fantastic).

Hi Leon; they aren't octals ... noval 9 pins. The Thunder 1 10" and 12" models and the Thunder 1 RVT are all powered with twin 6GW8s / ECL86s. It and the more common 6BM8/ECL82 are two tubes in the same bottle; a triode, exactly like half of a 12A_7, and a 'sharp cut-off' pentode power section - 6GW8 tube data sheet. Because of the manufacturing economics in the two-tubes-in-one-bottle format, both the 6GW8 and the 6BM8 were particularly popular in European table radios. As a result, Mullard, Siemens, Telefunken, Tungsram .. all the big Euro mfrs made the tube and, in my opinion, the best-sounding versions are used European versions.

Guild chose the sister 6BM8 tube in the stand-alone reverb amp in the RVT models while using the 6GW8 for power. I think whoever designed the T1 / RVTs was after a dry, tight tone and thought the 6GW8 better suited. In the late 50s/early 60s, the 6BM8 was used in Gibson's GA1RT, this beautiful GA8T, and Guild's RC30 remote reverb amp (functionally comparable to the Gibson GA1RT). Guild's T1 RVT reverb amp is a near part-for-part dupe of the GA1RT circuit. Univox later borrowed or licensed the GA8T / 6BM8 circuit in its U45B Jimmy 'Stairway' Page amp and 6BM8s appear in the Hilgen Meteor, another dupe of the GA8T circuit. Despite the similarities, the 6GW8 and 6BM8 are not drop-in substitutes. Can be done but must disconnect / relocate / reconnect 4 of 8 pins on each tube. John

Cool stuff cj. Muchas gracias!

8) J