KAY 754 Guitar Amp

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CJ

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not too many of these left,

series heater string death trap but we built an iso xfmr,

pic from the 67-68 catalog can be found at>

http://www.kayvintagereissue.com/downloads.html
 

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kind of like a 7 inch speaker, 4 ohm,  with ground lug,

we get a lot of squealing without the spk gnd wire, so if you have a squealer, you might try a speaker gnd, although most amps already tie one lead to the chassis, this had floating spk leads off the OPT,

 

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open heart sugery without atisthetic

home grown iso transformer with dual chambers for a 30KV hi-pot,  :D
 

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we added coax cable to the three input jacks, grounded at both ends ad the amp is quiet,

trem jack ft sw and we spliced some caps in place of the filter multican as seen on previous pic,

looks like we have a transistor hidden in here, wtf?
 

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no schematics available online, not tough to draw this guy,

12AV6, 35W4 half wave rect, 50C5 good for 2 watts,

2N3711 is the preamp, they wanted a tremolo amp but told engineering to do it without adding a tube which would screw up the series string heaters, so they swap the AV6 from preamp to Trem circuit, add in 3711 transistor preamp  to make the worlds first hybrid guitar amp, (maybe)

'starved plate" transistor circuit, 1 micro amp bias current, (see the 22 meg bias resistor) thought they stuffed 22 M instead of 2.2M but , we tried pushing more current thru the base but got distortion so i guess these guys had an inkling as to what they were doing, i guess  as this was the same time period when we put a man on the moon with a 8086 processor,

collector current is 1/3 ma, so hfe= 333

big drop down resistor to get the 1/3 mil to kill volts so we dont exceed the 25 volt V-ce rating of the 3711,

not a lot of high end, tried different tone cap no luck, probably the 3000 turns on the EI 50 pri-sec OPT , but lo-fi is what this is about,

we ditched the 100K and the .005 death cap after installing the iso xfmr,

ac and dc voltages show,
 

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here is a shot of the iso xfmr installed, added an IEC pwr jack to make hookup easy , gonna sub in a fuse model IEC after we order one,

78 EI core, runs cool but drops 120 to 110, too much DCR but the tubes don't mind,
 

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The speaker is indeed a now-odd size, familiar if you've pulled the radio in a 1941 Plymouth. May well be leftover car-speakers.

I have a cardboard Kent in the garage which is clearly the cheap model of your Kay. No "chassis", cruder PCB, and a 4-inch "speaker". Lessee if I can find a plan.
 

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> a 100 volt dc outlet on the side of a doug fir somewhere

First need a 1,700 mile extension cord to reach the nearest Douglas Fir. All pine and spruce here.

However if I find a Tree-DC outlet on a pine, all my electric chainsaws are Universal motor and will run on DC. I can cut all the spruce (before it falls down on driveway or garage). Except the switch is AC rated, so how many times will it break inductive DC?

Dunno what to do with my Kent. It is a Piece Of History which is probably best forgotten. I've considered re-scaling it with ~~62V DC to lower the power to suit the speaker and bedroom levels (62V also heats the bottles). But the vol-knob-first preamp is hissy crap. And I am sure the speaker is a reject from table-radio production. If I do an iso-tranny and put in a proper speaker (8 or 10), the investment is more than it would be worth. Developing a better topology with more features and a decent OT may be good money after bad. Maybe a chip-amp with a wall-wart from GoodWill? But I also have a 3/4-decent Sony AM/FM with a good speaker and nice case which would blow the Kent away on sound and looks.
 
PRR said:
Except the switch is AC rated, so how many times will it break inductive DC?

Clamp diode across the motor? Just make sure you plug it in the right way. ;-)

Triac-based variable speed trigger? New problem, won't shut off when released.

From the peanut gallery.

Gene
 
Gene Pink said:
Triac-based variable speed trigger? New problem, won't shut off when released.

Won't change the speed at all, always full... better use a direct connection and pull the tool away from the wall till it stops spinning.

JS
 
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