Model 50

[Default]

Incoming to Casa Default.
Basically, a mid-fifties Masteramp Model 60, but without the tremolo circuitry and the attendant 6SN7GT tube. Probable tube lineup of 2 @ 12AX7, 2 @ 50L6GT, 1 @ 35Z5GT half-wave rectifier. On some Guild amps using this tube set, there may be an additional selenium rectifier, which would rectify the neutral leg of the incoming power, reducing hum.

Incoming amp:





Previously sighted Model 50





Listing with more pics.

https://reverb.com/item/92901456-guild-model-50-masteramp-with-original-cover-1954-black-and-white

 

[GGJaguar]

Break out the isolation transformer.

 

[Default]

I have a bench isolation transformer. I'm very interested in the current draw of the total circuit. The first run of amps had isolation transformers for the b+, but not for the heaters of the 50L6s and 35Z5.
Still, it isn't the strangest circuit I've seen. Searching through the publicly available Sam's service materials, I saw a hifi design that used 6SN7s for preamp, phase inverter, output, and for the rectifiers. I didn't even know the latter was possible.

 

[Rocky]

I saw a hifi design that used 6SN7s for preamp, phase inverter, output, and for the rectifiers. I didn't even know the latter was possible.

Not commonly done, but i would think you could determine a vale of a resistor grid>ground that would give you a current limited rectification. Of course you would have limitations of plate diss, which I can't imagine is more than a few watts.

And not all amps with series string tubes were power-transforemerless. I had an old Harmony (H303B?) that shockingly (or not) had an isolation transfomer

 

[Default]

6SN7s are pretty sturdy, being an old radar tube. That particular schematic had two full tubes as a push-pull final.

The thing with isolation transformers in series string amps is a lot of times, it's only on the b+, not the heaters. If you replaced the safety/death cap with a fresh one, and replaced the two prong with a polarized two prong, you could skate by unless someone wired the hot and neutral backwards. Which was the case in my old apartment. You had that socket, and a properly wired and a correctly wired socket within a foot of each other...

 

[Rocky]

6SN7s are pretty sturdy, being an old radar tube. That particular schematic had two full tubes as a push-pull final.

Each triode has a max plate dis of 2.5 W. So a couple of tubes in push pull could conceivably do around 10W Class A to about 20W in Class AB. Pretty respectable for a triode output section.

 

[hearth_man]

Not commonly done, but i would think you could determine a vale of a resistor grid>ground that would give you a current limited rectification. Of course you would have limitations of plate diss, which I can't imagine is more than a few watts

I really like that approach! As long as the power requirements are low that is great outside the box thinking. Or at the least a non typical application of a twin triode.

 

[Rocky]

I really like that approach! As long as the power requirements are low that is great outside the box thinking. Or at the least a non typical application of a twin triode.

What is a triode other than a diode with a modulating grid?

 

[Default]

There are much more efficient tubes for that purpose, though. A 6x5gt pushes all the electrons you need and saves a socket. I just brought it up because it was Hella weird. 6SN7s are sturdy, but they don't offer much in the way of amplification. Replace all the preamp tubes in your Marshall with 12AU7s (the 9 pin version), and it won't chug at all.

 

[Rocky]

Replace all the preamp tubes in your Marshall with 12AU7s (the 9 pin version), and it won't chug at all.

It becomes a Hiwatt.

 

[Default]

So far, same board and components as used in the previous Guild amps, although this has what looks like two isolation transformers. There is a broken wire to one of them, so I haven't fired it up. Looks like there are three replaced electrolytic caps. 2 x 12ax7s, 2 x 50L6s, one 35Z5 rectifier.

 

[Guildedagain]

Looks like a pine cab?

Love the Silvertone knob, literally silver tone.

 

[Default]

Fingerprinted plywood cab. It sat in water at one time, so the bottom panel was replaced, poorly. Knobs are off the shelf for the period. I have a few Allied Radio catalog pdfs that offer them. Very similar to Emerson radio knobs.

 

[Default]

Output transformer is a "New York Transformer Co."
There are two transformers which are some type of isolation or filament transformers, made by William Brand & Co. Among other products, they made shielded wire and also the tubing used in WW2 aircraft superchargers. All the parts date codes are clustered in 1953-54.

 

[Default]

Link to W. Brand history.

Windham Textile and History Museum - Photograph, Electro Motive Plant, Willimantic

Aerial photograph of Electro Motive plant on Bridge Street in Willimantic, CT. (Electro Motive had two Willimantic plants, one on South Park Street and the other on Bridge Street. It built neither of them, but rather purchased former textile mills. The Bridge Street mill was first constructed in...

hub.catalogit.app

 

[Default]

The knobs are the same type as fifties Emerson knobs, except the Guild knobs have a recessed painted indicator dot.