The Infamous Kay 703C! - Help finding an output transformer? - diyAudio
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Old 14th September 2007, 08:05 AM   #1
ambrose is offline ambrose  United States
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Default The Infamous Kay 703C! - Help finding an output transformer?

Aloha, all... Ambrose here. New to the forum, so please take the slamming down a few notches for this thread. hahaha...

I've done enough tube amp repair work to know what a little nightmare the infamous Kay 703 can be, and as a working musician I know just how PHENOMINAL they are if you can get them purring and, well... safe haha...

My first Kay 703 was the first tube amp I decided to tear into to try and "soup up." It was actually working just fine, no serious hum, I was even playing it live in some small (and I mean SMALL) clubs... when one day, at an open mic gig some meathead told me that the little transformer mounted on the speaker could be lopped off for a volume boost. I wanted to upgrade the speaker to a Jensen Mod anyway, so not knowing much of anything back then, I cut it free (leaving what I thought would be enough length on each end to be able to re-plice).

Needless to say, chowderbrain that I am, I got my first ever whiff of bunt flesh that day hahaha... got shocked and GOOD... joys of being a young, dumb kid, I guess! Anyhoo, I tried to re-attach the transformer and ended up, well, destroying it.

I shelved this puppy and picked myself up another functioning 703. Years pass, and I damn near forget about it entirely until I'm pulling some old gear out of storage just this evening and I come across ol' shocky haha...

The amp is still completely solid, save for the transformer I mangled... I even still have all the odball tubes (including one 60FX5 that isn't ENTIRELY microphonic yet hahaha)... and, well, I'd LOVE to have two of these babies in my arsenal...

Does anyone know where I can get a replacement transformer for this? The schematic looks like no help whatsoever... printed on the transformer itself is the following:

280057
5A79
892431

I've googled these up together, seperate, and in any combination with no luck... Any help out there, to help repair the dammage done by my former, electrocuted self?

Thanks amigos!

-Ambrose.
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Old 14th September 2007, 08:26 AM   #2
EC8010 is offline EC8010  United Kingdom
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What are the output valves?
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The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
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Old 14th September 2007, 12:50 PM   #3
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Sounds like a 60FX5 or two.

All of the 60FX5's I've run across have been microphonic.
I built a headphone amp with a pair once.. 1W of ear-blasting insanity.
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Old 20th February 2008, 05:40 PM   #4
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Default Kay 703 Transformer

Hey Ambrose,
I am in a similar situation. I cut the speaker free so I could attach a 1/4" out on the amp, only to find out that transformer on the speaker is absolutely essential.

I was wondering if you made any headway on finding out info on the transformer. The first two lines of numbers on mine lead me to your post, but the third is different. I'm assuming the first two are model and the last is serial or something.

I realize that the other posts here did not help at all, but I was hoping maybe you got some assistance somewhere else.

Absolutely any help you can give me on this would be GREATLY appreciated.

Thanks again,
Jeremy
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Old 20th February 2008, 07:56 PM   #5
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Last line is the date code, so it will vary. I have a half-dozen similar transformers, all riveted to small speakers from '50's and '60s radios. And would probably destroy one trying to remove it... What you need is 2.5K primary, single ended, to your speaker impedance (usually 4 Ohms, but could be 8...).

But the REAL problem with this amp is that it isn't isolated from the power line. One leaky cap and your next contact with a mike stand could be your last! You can make it safe by adding a 50 VA isolation transformer ($15 from Allied) and a 3-wire power cord (both would be necessary to market a similar product today...)
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