1956 Guild Masteramp

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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.

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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.

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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.

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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.

IMG_0277_zps2a914cee.jpg
 

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The amp powers a Jensen P12P speaker.

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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! so now you have 2? and Zizala has 2? and I have seen a couple other similar examples out there recently. are these things just falling out of the sky all of a sudden? amazing.

edit...and Wilfred!
 

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Zizala's is the Model 66 with the 50L6 powertubes. Wilfred's amp doesn't have trem, so maybe a Masteramp unknown number. The amp I bought from GC is definitely a Masteramp 60, but I have not the slightest clue about this one. Guild was always coy when it came to actual specifications, so who really knows? The caps in this amp were all from 1955 or so, but there aren't any numbers on the trannies. :-/. I'll do some more work on it this week, but I have to decipher the caps on the board. They are so old that they have a stripe code on them. Guild used to spend time down in the surplus shops looking for the pushbutton switches for guitars. Looks like they built a few amps that way too!
 

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You're right of course, but That's what I get for posting on my phone at work. I should have drawn a better distinction. What the J/G models all have in common is the Ampeg-sourced chassis. And design, lol!
Guild amps seemed to get pretty consistant in construction when they went into production.

The pre-J's all seem to be hodge-podges of materials and build techniques. On this amp, I had to replace one side of the heater wiring because the insulation had broken down to the point where it looked like a string of beads. That was the only wiring in the amp that had deteriorated in that matter. It was almost like they were trying to figure out how to build a more powerful amp and doing it on the cheap.
 

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Hi Steve,

I don't know how I missed this....got the "archtop and hollowbody" tunnel vision syndrome it seems!

Very interesting discovery and observations......I'd been staring at that amp on Gbase for quite some time.
From my good fortune with and fascination with the Model 66, its oddity made it very attractive.

With all your amp technical and restoration abilities it looks like its gone to the right guy.
Keep in touch....I'd love to hear more from you about this one.

z
 

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It's going to take some tweaking, Z! Those 'bumble capacitors" are notorious for leaking dc, so the project for today is to replace them all with Mallories. I still need to repair the Jensen's cone, but that will go into storage and be replaced with something else.
What, I'm not sure. :-/ Right now, it has a 50 watt Yamaha installed.
 

zizala

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All good stuff.......keep it rolling while you can, so it doesn't get buried in the closet!

That Jensen is worth the expense of a good recone.....
For some of my old amps....for good age appropriate speakers in the meantime, I've enjoyed using some of those old Rola alnico organ pulls quite a lot.
Sometimes they just stay in there......

z
 

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Aquired another one today for a good price locally . Recapped, three prong plug, marked on the inside of the amp, "ok, 05/13/57 JB"
Same date on the speaker as the other one I own. This one is cleaner and still has the original cover.
 

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Aquired another one today for a good price locally . Recapped, three prong plug, marked on the inside of the amp, "ok, 05/13/57 JB"
Same date on the speaker as the other one I own. This one is cleaner and still has the original cover.

nice! Pics please!
 
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