Vintage Kay Model 754

[jnlfrazier]

Kay 754 Amplifier picked up at auction. I don’t know anything about it. Before tearing into it I wanted to know if anyone had any information on it. It doesn’t work and strange there’s no power transformer or anywhere to mount one, so I guess it came this way. Also, no fuse with it. Thanks.

[DrGonz78]

The fuse is one of the series filaments. Sounds like a widow maker.

[mozz]

With no power transformer, they are known as widow makers. Your chances of getting shocked are 50/50, depends which way you plug the 2 prong cord in. Tubes are series string filaments or a variation of, adds up to 110-120v. Best bet is to install a isolation transformer. That will let you hook up a proper 3 wire cord and you can also add a fuse. Mouser sells isolation transformers cheap.

[Chuck H]

Well I just joined "groupdiy" because some guy on there has this amp and hand drew a schematic for it. Unfortunately I have to wait until my membership is approved before I can upload it. So more to follow. In the meantime...

It's a "widow maker" to be sure. And only three tubes even though it has a tremolo.?. One rectifier, one preamp tube and one power tube. So where's the tremolo circuit? Well in the thumbnail pic on groupdiy I'm pretty sure I can see a transistor in the schematic!!! I think that would make this amp one of the earliest guitar amps to combine tube and transistor technologies. We'll see whenever my membership gets approved.

[jnlfrazier]

This is my first time working on a Widow maker. Iso transformer on order. Will also the fuse. Would love to see a schematic of the amp. Thanks for the information.

[dmeek]

Here it is, from groupdiy

[Chuck H]

Awesome dmeek! Thank you

[Chuck H]

Well it looks like I was wrong when I said "preamp tube" earlier. It's a preamp transistor and the tube is serving tremolo duty. That has to make this the earliest "hybrid" amp I'm aware of to date. Interestingly the transistor input is just a single transistor with no buffer. That's going to load quite a lot of capacitance on the guitar signal (fwiw). I'd be interested how it sounds once it's get's working. Though I might be inclined to lose the transistor input and rewire it more like the Kay 750 using the trem tube for the preamp.

EDIT: Or I might add a second transistor to act as an input buffer. Then you could keep the tube trem.

EDIT2: But safety and function first! Let's get it set up with an iso transformer and operating

[jnlfrazier]

Question. After I install the Iso transformer do I remove any caps and or replace with x caps?
Also can anyone tell me what kind of speaker this is? Doesn't match any codes I've seen.

[jnlfrazier]

Speaker post.

[Chuck H]

What are "x caps"?

Any capacitors in that amp will be OLD. The electrolytic capacitors may well be (probably are) bad and would need replacement. Film and ceramic caps may be fine.

The information on the magnet frame may only be speaker MODEL information. I usually see manufacturers codes on the rim of the speaker. And I don't see anything in the image, but I can't see the whole frame either. A lot of Kay amps used Magnavox speakers. Which sound just fine IME but are realtively low efficiency.

EDIT: Well I just looked up a bunch of old Magnavox speakers. The used a lot of different frame styles but your speaker doesn't look like any of them.

EDIT 2: 1056 is the old speaker code for Fisher. The frame doesn't look like any Fisher frames either though.

[jnlfrazier]

Class-X and Class-Y safety capacitors are used to filter AC signals and reduce EMI. To do so, however, they must be connected directly to the hazardous AC line voltage which requires that they be certified as “safety capacitors” to verify that they are safely operable under this condition. There are various form factors of safety capacitors that are used in safety-specific filtering circuits. Although not exclusively used as such, ceramic surface-mount and ceramic disc safety capacitors are commonly used for interference suppression AC line filtering applications while film capacitors are more often used for conducted emission attenuation.

[Chuck H]

Ah. Yes I know about CLASS X and Y safety capacitors. I missed the reference without the word "class".

With the iso transformer and a proper safety ground there is no typical application for safety caps. Ideally any caps that go to chassis after the upgrade would be going to earth.

And... Still no ID on the speaker but I did look at two other 754's and they both have the same speaker as yours. I did see a pair of "Heppner" speakers that had the same frame painted in black. It's a fun corker but I'm not finding an answer for it.

[TomCarlos]

EDIT 2: 1056 is the old speaker code for Fisher. The frame doesn't look like any Fisher frames either though.

I agree with Chuck.... This is an old Fisher Speaker. After 1974 (give or take), "1056" was an identification for "Gefco." These speakers were also used in Silvertone, Airline, Danelectro amps.

[jnlfrazier]

You guys are a wealth of excellent information. I really appreciate it.