Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Steve_P on November 25, 2013, 07:26:18 pm
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Picked this one up from Kummers Vintage. I changed out the B+ filtercaps and subbed in caps for the cathode bypasses. Very interesting amp as it appears to predate the 66J and the 99-100J series of amps. It has no model ID anywhere on the amp, only "1366" on a piece of tape on the baffleboard. The covering is the typical TV front woodgrain shelfpaper on the bottom and the top is a white elephant hide tolex. The grillcloth is a simple brown.
(http://i1159.photobucket.com/albums/p627/Steve_CPhillips/1956%20Guild%20Masteramp%20Mysteryamp/IMG_0278_zps2f4db65e.jpg)
The amp is powered by two 6L6s, but the construction is unusual for Guild. The power transformer is bolted to the bottom of the cabinet, and the chassis (such as it is) contains the bias supply, the filter capacitors and has a 5U4 rectifier mounted. It is connected by an umbilical to the upper chassis.
(http://i1159.photobucket.com/albums/p627/Steve_CPhillips/1956%20Guild%20Masteramp%20Mysteryamp/IMG_0271_zpsd7b7f9a9.jpg)
The upper chassis appears to have been the same used for the Model 66 (not the "J" ) which is a transformerless ac/dc amp. However, this chassis does not have a hole punched for a rectifier, which the the Model 66 would have. Strange. The sizable output transformer is mounted in a cutout above the powertubes.
(http://i1159.photobucket.com/albums/p627/Steve_CPhillips/1956%20Guild%20Masteramp%20Mysteryamp/IMG_0265_zpsd3cba8e5.jpg)
The control panel is identical to the Model 66, having two volumes, bass and treble, a two position tremolo speed switch and speed and depth controls. The green pilot light and the power and standby switchs are on the left side of the control panel.
(http://i1159.photobucket.com/albums/p627/Steve_CPhillips/1956%20Guild%20Masteramp%20Mysteryamp/IMG_0277_zps2a914cee.jpg)
The amp powers a Jensen P12P speaker.
(http://i1159.photobucket.com/albums/p627/Steve_CPhillips/1956%20Guild%20Masteramp%20Mysteryamp/IMG_0270_zpsd6576e07.jpg)
(http://i1159.photobucket.com/albums/p627/Steve_CPhillips/1956%20Guild%20Masteramp%20Mysteryamp/IMG_0268_zps9160993e.jpg)
220626 indicates that the speaker is a Jensen manufactured in the twentysixth week of 1956. This is the newest part in the amp, so I feel confident that this amp predates the Jazz series of amps. This amp is interesting in that it uses a "fixed" bias that supplies a negative voltage to the screens of the 6L6 output tubes. Most Guild amps that I have knowledge of use a cathode resistor to bias the tubes. The fixed bias method was not used by Guild until the Aaron Newman-designed Thunder series debuted in 1963.
After some limited playing time, I'm pleased with the tone of the amp, but it obviously needs some additional TLC. The tremolo caps are probably going to need replacement and most of the grounds need to be cleaned of almost sixty years of corrosion. The Jensen has a hole in the cone - I may just have it reconed instead.
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Nice amp!!
... I'm pleased with the tone of the amp, but it obviously needs some additional TLC. The tremolo caps are probably going to need replacement ...
View the bumblebee caps with suspicion; they are notorious among radio restorers for leaking d.c.
You might do some careful d.c. measurements around them to confirm they are not leaking & upsetting the bias of stages.
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I was going to replace the whole lot. I have no doubt that a bunch are leaky. The amp sounds woolier than it should. I have the 1963 version sitting right next to me and it's a loud, clean jazz machine.
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Nice acquisition!
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Dig vintage amps. What price is it in?
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Dig vintage amps. What price is it in?
Not sure what you are getting at. Come to think of it, I wasn't sure what I was getting when I bought it!
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I think what he was trying to say in a round-a-bout way is "How much did you give for it"?
But I might be mistaken! Anyway nice purchase! I love restoring something like that. platefire
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I paid a c-note because it wasn't working. On those bumblebee caps, can I cut out enough of the body of the cap to epoxy it over a Mallory, just to keep the look? More of an idle thought than anything else. I already replaced the can cap, but the cardboard sleeve on the old one popped right off, so I put that on the new cap.
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On those bumblebee caps, can I cut out enough of the body of the cap to epoxy it over a Mallory, just to keep the look?
Check them before ripping them out. Odds are they're bad, but no use wasting them if you don't have to.
Those caps have a seam where 2 halves were joined over the original innards. I dunno if the casing is adhered to anything on the inside. Seems like you could take an X-acto knife and slice the case open, then re-glue around a different cap.
It would be sleazy if you did that and didn't tell the next owner (if it ever sold), but only because some people get all hyped about those caps. Radio guys re-stuff cap bodies with modern parts all the time to maintain cosmetics.
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Hi guys, I cheated with a couple I singular cap cans and dug out the guts and fitted new electros. :icon_biggrin:
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I'm not sure 'cheating' is the right statement? after all, you spent the time to clean and stuff so that would be more like 'hard' work to me.
Cool vintage amp there amigo. I love those old Jensen concert spkrs but be very careful becuz they can shred even at low volumes.
:icon_biggrin:
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Thanks, guys!As for stuffing the old caps, I haven't seen bumblebees used as extensively in Guild amps before this one. I wanted to keep the look the same, but have a functioning amp too. It looks like some sort of Weber will be going in there to save wear and tear on the Jensen, which has a hole in the cone already.