To 'Bay or not to 'Bay: Thunderbird Auction

JazzWest said:

Here's my '69 Guild Thunderstar amp (which I'd like to find a good home as I just do small gigs that my little Thunder I covers it) ... the Thunderstar it had a sweeter, compressed tone, like a Fender Vibrolux. Maybe the 12DW7 phase inverter used by the Thunderstar has to do with the sweetness? I do have a schematic for the Thunderstar that I purchased from Musicparts.com.

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Thanks JW; great looking amp! Email sent. cj

Hi Capn & John,

Take a look at your Thunderbird schematic. Contrary to popular belief I am pretty sure the Guild amp "tone switch" offers passive filtering for two settings and one is flat.

I think you will find only find R's and C's in the network. Based on the tone sound one is a HPF (bassey setting) and the other is a LPF (bright setting). The center setting is probably flat. Guild literature indicated one was Bright, Flat and Bassish.

I am glad to see all getting turned on by this amp. I heard my first Thunderbird around 1967 and always wanted one. It took me 25+ years and the internet to get mine. (I used to bug an old friend who had one every year around Christmas when our two families would meet at our home town for Midnight Mass.)

The Thunderbird is sweet sounding at low settings and when cranked up sounds British with some bite. The 7591A sound outstanding when pushed. I have a preference for all of the Guild amps that used this power tube (i.e., Thunderbird model 1 & 2, Thunderstar, Maverick).

M

matsickma said:

...Take a look at your Thunderbird schematic. Contrary to popular belief I am pretty sure the Guild amp "tone switch" offers passive filtering for two settings and one is flat....I think you will find only find R's and C's in the network. Based on the tone sound one is a HPF (bassey setting) and the other is a LPF (bright setting). The center setting is probably flat. Guild literature indicated one was Bright, Flat and Bassish.

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This is the tone switch Mike is referring to from the Thunderbird schematic; each channel with its own switch:



The switch is in the 'flat' or 'null' position; when moved to the next position, the signal sees the .01uf 'high pass' cap for bright/more treble, and one more position to the visual right, the signal sees the .033uf 'low pass' cap for more bass.

Having a hell of a time pasting a picture from the schematic. Help me out with more.

What you've shown there, and what Mike refers to, is the "A" side of that three-position slide switch. There's a "B" side as well, at the top of the schematic a little farther to the right. Can you decode that one for me as well?

As we say in Norway, mange takk.

john_kidder said:

What you've shown there, and what Mike refers to, is the "A" side of that three-position slide switch. There's a "B" side as well, at the top of the schematic a little farther to the right. Can you decode that one for me as well? As we say in Norway, mange takk.

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Du er velkommen jeg tror. This is the other switch shown in the schematic; I think this is the Bright switch:



Interpretive text edited out; see do-over further on down. cj


All this Thunderbird talk is getting me GASsed; I have some nice looking cypress that would make an extremely bueno cabbie ... unless you are just angry, ya doesn't have to put T#1 back together again ya know.... :wink:

Regards,
John

capnjuan said:

matsickma said:

... I am pretty sure the Guild amp "tone switch" offers passive filtering for two settings and one is flat....I think you will find only find R's and C's in the network. Based on the tone sound one is a HPF (bassey setting) and the other is a LPF (bright setting). The center setting is probably flat. Guild literature indicated one was Bright, Flat and Bassish.

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MESSAGE 1, re Switch Side "A"
This is the tone switch Mike is referring to from the Thunderbird schematic; each channel with its own switch:

The switch is in the 'flat' or 'null' position; when moved to the next position, the signal sees the .01uf 'high pass' cap for bright/more treble, and one more position to the visual right, the signal sees the .033uf 'low pass' cap for more bass.

MESSAGE 2, re Switch Side "B"

As shown, it looks to be in the 'null' position; signal loops up, across the contacts which offer the least resistance, and then downstream after the R/C network; the signal never sees the R/C network.

The 'middle' position forms a 'dead head' going nowhere and the signal sees both the .001uf cap to ground and the resistor 'sort of bright'; if I understand correctly, this allows some lower frequency to stay in the signal.

In the rightmost position the switch contacts, because they offer the least resistance, form a bypass around the resistor and the signal is connected to the other .001uf to ground beyond the resistor 'bright'.

The function of the caps are to suppress lower frequencies; the middle position provides an alternate path, the 3rd doesn't.

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Hokay, I begin to have a glimmer. Tusen takk.

• Switch in flat position (to the left in the diagrams), no effect either Side A or B.
  Switch in middle position, Side A makes brighter, Side B pushes signal through the RC network to keep some lower frequencies.
  Switch in right position, Side A adds bass, Side B goes around the RC netwrok to be affected by only 1 capacitor, hence "brighter".

So doesn't this tend to give the two sides a bit of a "neutralizing" effect? Side A affects the signal before the first half of the first 12AX7, Side B affects the output from there with the opposite effect?


And you're right, I don't need 2 Tbirds, although it would be beyond cool to have one here in the city and one up-country - even one does take up a lot of room in the car, and the dogs complain (not, or course, my dear wife - she just suffers). I'll think about it some more, and get some photos for discussion.

you're right, I don't need 2 Tbirds, although it would be beyond cool to have one here in the city and one up-country - even one does take up a lot of room in the car, and the dogs complain (not, or course, my dear wife - she just suffers). I'll think about it some more, and get some photos for discussion.

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Bigger car? Tie dogs to the roof? [gubernatorial precedent for that, here in US]

Going to do it over John, I think I bunged it up; if I stare too long, it all starts to wiggle around like spaghetti with stuff floating in it. I think I have the Tone switch interpreted correctly, getting squirrelly with the Bright switch.

Ya know, years ago they instituted T-Bird rationing in Canada; 1 man, 1 Bird; I'd hate to see you get in trouble and everything.... :wink:

Thunderbird amp; Bright Switch Positions

Best I could do John, maybe Mike will straighten me out...his engineering many more way better gooder than mine. In the null position, the contacts in the switch form a bypass around the R/C filter. In the 'moderate' position, the entire filter is functional and if I'm interpreting it correctly, in the maximum position, the two caps are in play but the resistor isn't. If I have this right, 'moderate' means some bass signal gets through the resistor but, if the resistor is 'jumped out' (Pos 3), then the signal sees only the bass-suppressing, high-pass caps....maybe or not ... Don't try this at home folks!

Bump, back to original posting about listing for Thunderbird "15" main, dual 8" w/o reverb tank"

I inquired about how someone had managed to get a 15" and 2x8" speakers into a frame with just enough room for 1x12" and 1x8", and about the Seller sent me these pics.




Note the (larger) plywood baffle, the new height gained by taking the 15" all the way to very edge of the chassis, and the cuts in the frame required to get the fit. Note also the apparent moisture damage to the cabinet in the lower left - beware when shipping this puppy.

The reverb looks to me as if it must be the regular spring tank version - the leads to the two reverb speakers are obvioulsy carrying the same signal (the bottom 8" Jensen has no signal return?)

Fun, huh?

Hi John; I'm probably a little more anal than most amp hacks but I use a paint brush to sweep out the carpenter chips...maybe they're mesquite for the Tex-Mex thing. I see that he gained the horizontal space by using the smallest width battens possible but I question whether this amp has spring reverb at all; the schematic i have and ealier colored box pic in this thread shows a can; i.e., it isn't done electronically.

One of the immutable laws of matter is that everything that exists does so somewhere in space and time (not my law, I read it on the side of an Esteban guitar box). Where is the reverb can in your model?

We can see that the can isn't on the bottom of the cabinet. We can (more or less) see that it isn't on the visible side of the tube deck where the shortest tanks, 9" or so, might go. See pic below: a reberb can; mounted on the tubedeck of a Silvertone 1484 - on the visual right behind the lineup of three shielded tubes:



Unless the can is mounted on the underside (component side) of the chassis which I don't think was ever done, I don't know where the can is. Unless there is a 'black box' somewhere creating a delay, I think somebody 'cowboyed' this amp.

I was also a bit astonished to see the wood chips and sawdust lying around. If the amp's been "in storage" for 30 years, one might think that the storer would at least have blown the debris out before putting it away. As it is, the cuts look fresh enough that one might think the amp had very little, if any, use before being stored?

I'll pull the chassis out of my TBird tonight and locate the reverb. Again, I seem to recall Mike telling us something about the can being located w/in the chassis, and my memory tells me that the (still) broken TBird 1 had the can located much the same as that Silvertone.

But even if there were some sort of black box electronic delay in the one on offer, beats me how one could get a reverb effect with the two speakers (apparently) being fed by the same leads?

And, for an old cowhand like myself, let's restrict the use of terms like "cowboyed this amp" if we can (joke). I once had a boss who asked me to perform a business transaction that was barely this side of legal, but was clearly unethical. I flat refused, and he said "Hell, Kidder, I thought you were a cowboy!" I responded that what cowboys really did was to take care of cows and little baby calves - nurturing, in touch with our feminine sides, the very picture of the noble chevalier and the knight at arms, and all that.

I am, however, willing to say that someone "farmered" the amp, that seems certain.

john_kidder said:

I was also a bit astonished to see the wood chips and sawdust lying around. I dunno; sometimes they just don't think; they 'look' through the viewfinder but don't 'see' - motorcyclists will tell you the same thing about car drivers.

I'll pull the chassis out of my TBird tonight and locate the reverb. Again, I seem to recall Mike telling us something about the can being located w/in the chassis, and my memory tells me that the (still) broken TBird 1 had the can located much the same as that Silvertone. It is where it is ... if it is.

But even if there were some sort of black box electronic delay in the one on offer, beats me how one could get a reverb effect with the two speakers (apparently) being fed by the same leads? Despite what the seller says (he was probably stumped like me; no 'can' in plain view) the effect isn't done with doubling the speakers; it's just two speakers in parallel; they get the same signal, 'verbed' or not, at nearly the same time.

And, for an old cowhand like myself ... , let's restrict the use of terms like "cowboyed this amp" if we can only if we have to and I'm willing to make an exception in this case. I once had a boss who asked me to perform a business transaction that was barely this side of legal, but was clearly unethical. I flat refused, and he said "Hell, Kidder, I thought you were a cowboy!" I responded that what cowboys really did was to take care of cows and little baby calves - nurturing, in touch with our feminine sides, the very picture of the noble chevalier and the knight at arms, and all that. I am, however, willing to say that someone "farmered" the amp, that seems certain. 'Farmered' it is.

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The can in the bottom creates a physical conflict between screwing down the can and fastening the baffleboard to the cab; see earlier remarks re/ space and time. If the can were elsewhere, that would be a work-around for the conflict; if the T-bird chassis is deeper by several inches, that would provide the space.
cj

capnjuan said:

sometimes they just don't think; they 'look' through the viewfinder but don't 'see' - motorcyclists will tell you the same thing about car drivers

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Tell me about it - up until November '05, I was a bicycle commuter here in Vancouver. I used to make jokes like Q:"How can you tell if someone's a safe urban cyclist?" A: "They're alive."

Then a gentleman drove through a red light, not an uncommon occurrence, while I was in the intersection. You mentioned earlier the physical impossibility of two objects occupying the same space at the same time - I'm here to verify through empirical experiment that the hypothesis is correct. And when one object is a Toyota van and the other a soft human on a bicycle, one can easily deduce which object remains in the space and which is ejected. Major concussion, still causes me memory and functioning issues, various body bits not quite right, especially picking fingers on the right hand. No bicycle any more - the thought just freaks my wife out. And I am positively impolite to cyclists without helmets - I would certainly have been dead without mine.

All this on a bicycle decked out with multiple flashing lights and retroflective decals, wearing a bright red jscket with more reflective strips. No eyes, no brains, them bastids.

john_kidder said:

capnjuan said:

sometimes they just don't think; they 'look' through the viewfinder but don't 'see' - motorcyclists will tell you the same thing about car drivers

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All this on a bicycle decked out with multiple flashing lights and retroflective decals, wearing a bright red jscket with more reflective strips. No eyes, no brains, them bastids.

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Once a week, someone on a motorcycle or Haitian motorcycle (bicycle) here in Palm Beach County is struck/killed by a no-see-'em 'bastid'. Ugly...

Hi Guys,

The first two Guild Thunderbird amp models and the Superbird amps did not install a reverb "pan" in the cabinet as is done on most amps. Instead they installed a reverb "tray" up inside the amp housing. A reverb "tray" is basically the part of the reverb unit that makes the reverb sound. The tray contains the springs, input and output transformers and suspension system for the spring assembly. The "pan" we are used to seeing is a packaging item to hold and protect the reverb tray. Reverb pan's take up a lot more space. Guild elected to incorporate the reverb tray up inside the amp housing and not in the cabinet. I suspect that because these model amps use circuit cards it was easier to mount the trays close to the electronics. You can purchase reverb pans or trays today form Sound Enhancment Products, Inc. Guild used Gibbs reverb units. Gibbs were the origional units initially developed for the Hammond Organ company. Today you would replace it with a Accutronics model. Gibbs reverb units are identified by a single letter that is stamped on the back of the tray. The people at Sound Enhancment Products can usually crossreference a Accutronics unit for many Gibbs units. I included a picture of a 2nd model Thunderbird preamp assembly with the reverb tray. (Note: The tray in the picture is missing a series pair of springs. one side was damaged. I am currently getting a replacement.)



M

Also...IMHO the addition of the 2nd 8 inch reverb speaker is overkill and will result in more depth of reverb than you may want. If I owned this amp :twisted: I would alter the setup a bit. I would disconnect the 2nd 8 inch speaker from the reverb channel. Then I would connect it to the external /alternate power output tap coming out of the TBird. My rationale for this change is a) a single 8 inch speaker is plenty for the reverb effect and b) the 15 inch speaker may not be have a wide enough frequecy range to fully exploit the brightness of the Thunderbird. The addition of a bright clean 8 inch speaker would allow you to get a full array of sounds out of this amp from full low end to bright upper end. For this to work right may require the addition of a seperate rheostat volume control of the 8 inch speaker.

M

Wow, you guys have been busy since I've been gone!!

I've been thinking about buying this amp, but if one of you guys wants to take a run at it, I'll gladly step out of the way.
Just let me know, because if I don't hear from anybody, I'll may start bidding with about 10 seconds left on the auction.
Snipearoo!!

Gents, I've gotten the same pics from the seller. I also asked him to pull the chassis and give me a pic.
No such luck, though the seller did provide his phone number, instead. That's nice, but doesn't provide a picture of the chassis.
I'm sort of expecting that the reverb pan will be in there (not withstanding the auction language to the contrary), but you never know.

Here are the variables I'm considering:

Speakers: two Jensen speakers and a CTS speaker.

A) The 15" is a '67, not a '57 (as the Seller believes). It's a model C-15PS speaker, coded 220749.
It's a ceramic magnet Jensen, so it wouldn't be manufactured in the '50's.
Therefore, in this case, number code 220749 means:
1) 220= Jensen EIA code
2) 7= '67 year of manufacture
3) 49= 49th week of the year, while
C-15PS means:
4) C=ceramic magnet
5) 15=15" speaker size
6) P is the letter speaker grade; stronger than a Q or an R (found in Fender 4x10 bassman amps, Qs in the later ones, that is,
'59 or '60) but weaker than an N model (found in Twin Reverbs and Epiphone EA-300 RVTs)
7) S is for Special. A senior member of the LTG 'amp advisory board', who resides in Fla., but shall not otherwise be named or
mentioned, tells me that PS speaks were found in Dano and Silvertone amps (did I get that right, CJ?). If that's the original
cone and it's in good shape, it's may be a nice speaker for a guitar amp. On the other hand, Jensen was making some
pretty stiff cones by '67 (at least on a pair of '67 C12Ns that I passed on). Combined with a 15" size, that might not sound
great. Probably not terrible, maybe good, but not the best 15" speaker you ever heard......

B) The 'silver' 8" Jensen looks like the kind of speak found in Champs/VibroChamps. Wonder what the ohm rating is?
It would be a 4 ohm speak if it came out of a Champ. Wonder what kind of ohm load the amp is seeing from those 8" speaks?

C) The CTS speaker looks just like the one in my Thunder 1 RVT. The speaker code 137 548 means:
1) 137= EIA (Electronics Industry Association) code for CTS (Chicago Telephone Supply)
2) 5= '65 year of manufacture
3) 48= week of the year manufacture

Speaker $ value:

If I were gonna buy this amp, I'd value the two Jensens around $100, if they turn out to be in good, original shape.
'I'd give em a good getting rid of', as we say in Texas, take the money and buy a good 12" speak, after getting the template for a new particle board speaker-baffle from one of the brotherhood.

Speaker-board grille:
That's the original stuff, but it looks wavy and loose on the dark-side edge. I wonder if it's been cut a bit short and will always show the edge of the baffle on the sides?

Shipping:

Well, I'd pay more for shipping than the Seller wants and get him to ship the speakers and tubes separately.
I'd leave the plywood baffle-board in place, because it might help keep the crumbly Particle-board cab together.

I don't know if I'd ask the seller to take the chassis out and ship it separately (depends on his ability to pack a bare chassis), though that would certainly be the best bet for getting the cab in one piece and the chassis from breaking loose and rolling around. Particle-board cabs can have bad mojo, for sure. Somebody sees some water damage in a corner, right? That could be really bad in shipping, right?

Chassis:

There's no telling what's going on in the reverb section. It might be simple, it might not. $$$???

Finally, go back and look at the big Power Transformer in the pic that John Kidder provided. Why?
The paint is dripping off the trannie. Anybody think that it got really, really hot, like there's been some kind of 'thermal transformer event' that took place when a power tube socket arced, or something??

I dunno, maybe I'm wrong. 10 years ago, I would have looked at the PT and thought, 'Wow, they didn't paint it very well at the transformer plant.' Now, I just suspect 'foul play'. Old age breeds fear and paranoia, don't it??

gilded

Well now, ain't this fun.

If you're going to go for it, Gilded, I won't. I'm not surprised that the seller is a little leary of pulling the chassis - he might be just a bit surprised with some asking for detailed internal measurements and wiring diagrams for the speakers with arguments about his "electronic reverb" claim, and others saying "just pull the chassis and take a look". Poor guy thought he was just going to list and sell an amp full of wood chips.

I remain befuddled - if the two 8" speakers are 8ohm wired in parallel, doesn't that drop the impedance to 4ohm overall? And what does the reverb power circuit do with a 4ohm load when it's designed for 8? (Pardon my deep ignorance here)

I like M's idea for the second 8" speaker.

If you do buy it, Gilded, I will happily measure and trace the Tbird baffleboard.

On the other hand the Captain has been expressing a desire for a Tbird.

In any event, I won't be on the bid.

Cheers, everyone, always a pleasure,
John

Look at that - all of a sudden it's at $300 with 12 hours to go. No accounting for tastes, I guess.