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Unholtz-Dickie amp, 4-1000's
Unholtz-Dickie amp, 4-1000's
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Old 21st April 2013, 03:01 PM   #1
opcom is offline opcom  United States
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Default Unholtz-Dickie amp, 4-1000's

Found recently is a badly stripped Unholtz-Dickie 'shaker' amplifier. I am told by the strippers that it had a pair of 4-1000's. It ran on 3-phase power and used six 866's and two smaller MV rectifiers. It also used four EL34's as drivers. One person said the drive was to the 4-1000 screen grids from the EL34's.

Unfortunately the only components left are the chassis a massive vetical frame, the front and back covers (also cover the sides), the precious output transformer, and the 4-1000 tubes.

All the rest, the wiring, other iron, other tubes, a "phenolic circuit board" as said by the stripper, the tubes sockets were on, the 4-1000 sockets, the meter panel, etc are gone. Probably never to be seen again.

All is not lost. With the OPT in good cond., the 4-1000's,which I am familiar with for RF, and a donated plate transformer of 7500VCT @ 3.75KVA, I think this can be put back together so it looks nice and works fine.

Because so much is missing,it will be like the six million dollar man.. I would like to make it as much like the original in performance as possible.

There is an Unholtz-Dickie amp with 4-400's featured on youtube. I think this one is basically the same.

So, why not try to put it back in operation with new insides. It would look nice on casters in my living room.

So the begging goes out for the manual or schematic for one of these. Unfortunately there's no nameplate, so I can't even name the model.

I've done a resurrection like this before, but on a home-made 1KW AM transmitter found in a scrap yard. The reason I want a schematic is to better see how the drive was done.

Thank you!

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Last edited by opcom; 21st April 2013 at 03:05 PM. Reason: pictures
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Old 21st April 2013, 03:19 PM   #2
GoatGuy is online now GoatGuy  United States
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That is NOT an output transformer, sorry.

It is the power transformer. The word "plate" has to do with the fact that it is for the plate power.

I'm afraid you just got a box of iron and some copper.

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Old 21st April 2013, 05:22 PM   #3
opcom is offline opcom  United States
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That's incorrect. You have glanced at the Amertrans plate transformer nameplate. If you look at it for real then you will see it is on a black thing, which is obviously the Amertrans plate transformer, which is the only big black thing in the other picture beside the cabinet.

The big gray thing is the OPT and the three white terminals are plate-HV-plate. If I took time to find the video this would be obvious as it is what's connected to the output tube anodes. The video may be linked from an amfone.net topic not sure where I saw it.

You are right about one thing, I did just get a box of iron and some copper. Its exciting.
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Old 22nd April 2013, 06:26 AM   #4
Gilgy is offline Gilgy  United Kingdom
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Just going by what the nameplate says then I'd be inclined to call it a power transformer. 115 Volt primary 50/60 Hz doesn't sound like an output transformer!
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Old 22nd April 2013, 06:49 AM   #5
trobbins is online now trobbins  Australia
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That's a serious single-phase HV power transformer for starters -I hope you've got a good mains incomer with a bit of inrush suppression!

Is the OT oil filled? Or should I say 'was' the OT oil filled :-)

Have you got a suitable HV tester to check the insulation - omg, the practicalities of a renovation just keep getting harder and harder .....
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Old 22nd April 2013, 04:43 PM   #6
opcom is offline opcom  United States
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The nameplate is for the power transformer.

The output transformer was oil filled but it was drained and will be refilled with modern transformer 'oil'. I prefer to wait until it has oil in it again and has been warmd up a little to work the oil in before trying any hipot tests.

This site has a Philips-made amp, similar but a smaller one:
EL6471 1kW Großverstärker (Type 102408)

It looks like Philips and Unholtz-Dickie made the same design, perhaps for different regions as this one is from the USA.

Looking at the chassis for the Philips, it is about 60% the height of this one here and the OPT covers only 2/3 of the rear of the chassis. The one here covers the full width, so I would assume it is a little more powerful. It looks like the original mains transformer for mine is supposed to be mounted horizontally across the back of the frame near the bottom.

I may have a 3-phase mains transformer to fit it, although I gave it away I can get it back. It may also be possible to use a smaller plate transformer than the substitute I was given, which is from a WWII military transmitter. It would have to go on a 30A circuit, but the way I see it, if this can be made to work again, the electrician cost won't seem too much.

Unholtz Dickie has an office in California. Possibly they might help if I can find the model number of this thing on the chassis somewhere.
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Old 22nd April 2013, 10:40 PM   #7
trobbins is online now trobbins  Australia
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Top stuff - that link shows the layout beautifully.

Yes, you'd need an industrial connection to just run 1ph, plus then have extra filtering hassles. I guess you could use a separate enclosure for 'modern' bits like circuit breaker and phase-fail relay, to keep the original 'patina' of an old build.

Do you have any idea of the frequency range of the older vibration tables, and the impedance of a drive winding, and whether it was just one axis output or did they use three separate windings and how that was managed?

Are the plate and ht bushings on the OT still ok?
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Old 23rd April 2013, 12:43 AM   #8
TheGimp is offline TheGimp  United States
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Man, that is some serious iron.

Good luck with your project, and keep us posted.

I expect this will stretch out a while.
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Old 24th April 2013, 12:14 AM   #9
opcom is offline opcom  United States
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As far as I know the old shakers went quite low, maybe to 10Hz. It would depend on how much power was needed, right? I guess the things came with a spec sheet describing the operating conditions.

The voice coil connections are unknown. There are some 14 connections for that side. It's my expectation that some combination will match some sort of speaker.

All the HV bushings are fine. I have no idea how many axis and guess just one. From what I understand about some old shakers, there could be another cabinet full of reactances to shift the phase of the output signal so that application to two axes might make an elliptical motion, but none of that is clear just speculation. I have stripped some ex-military shaker drive matching cabinets found at Goban Supply in Chicago. They were full of 13KVA variacs, banks and banks of 440V and 600V oil caps, and giant rheostats.

I took some info from the Unholtz Dickie amplifier.
Type 129040
Nr. 639

Original tube compliment:
output tubes QB5/1750 (x2) (someone subbed 4-1000A's)
driver tubes EL34 (x4)
HV rectifiers RG3/250A (x6) (someone subbed 866's)
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Old 24th April 2013, 01:55 AM   #10
jackinnj is offline jackinnj  United States
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Unholtz-Dickie amp, 4-1000's
Screen grid modulation was used as an inexpensive way of getting high power a.m. You didn't need the expensive modulation transformer.
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