[Amps] Fw: Revamping a really ugly amp

la7sl Nils Petter la7sl at norgespost.no
Sat Mar 13 13:25:35 PST 2010


----- Original Message ----- 
From: "la7sl Nils Petter" <la7sl at norgespost.no>
To: "Dave White" <mausoptik at btinternet.com>
Sent: Saturday, March 13, 2010 10:21 PM
Subject: Re: [Amps] Revamping a really ugly amp


> Hmmm....
> a stepmotor, a controller and a rotary switch is a better idea !!
> (remove that "click" thing :-)    )
> And probably less expensive....
> I would not try cheap relays !!
> Vacuum could work...but would be very expensive at the required
> voltage and current ratings.
> A stepmotor, controller and roller inductor is also good...
>
> ----- Original Message ----- 
> From: "Dave White" <mausoptik at btinternet.com>
> To: "Rex Lint" <rex at lint.mv.com>; "Amps" <amps at contesting.com>
> Sent: Saturday, March 13, 2010 10:02 PM
> Subject: Re: [Amps] Revamping a really ugly amp
>
>
>> The only amp I've seen that used relays for tank coil switching was on 
>> the fleamarket at Friedrichshafen one year. I think it was built by a 
>> Hungarian guy and used Russian vacuum relays.
>>
>> I can't particularly think of a reason why you couldn't make this work, 
>> though someone may correct me.
>>
>> On 10m in particular there can be a higher Q and thus consequently high 
>> circulating currents, so you'd have to ensure enough current handling 
>> capacity  I can't remember what bands the Hungarian amp worked on, nor 
>> the chap's callsign.
>>
>> I do ask the question, however: if it's a piece of cake, how come no-one 
>> else does this?
>>
>> Good question, though - and one I've asked myself a few times!
>>
>> Dave G0OIL
>>
>> -----Original Message-----
>> From: "Rex Lint" <rex at lint.mv.com>
>> To: "Amps" <amps at contesting.com>
>> Sent: 13/03/2010 20:04
>> Subject: [Amps] Revamping a really ugly amp
>>
>> I bought an old H/B amp that I'm totally revamping.
>>
>> It's 2 x 3-500Z's with a 4KV power supply.  It USED to have a pi-network
>> with a vacuum variable plate capacitor and a regular variable loading
>> capacitor, and the tank coil *was* a variable inductor so that the tank
>> could be adjusted for any transformation (within reason).  I want to keep
>> the caps, but change the coil to discrete inductor(s) with taps.
>>
>> I wonder if anyone uses relays instead of a rotary switch to select the
>> desired taps?  What are the parameters I need to consider in trying this?
>> In my thinking, I'll just be switching the output side of the inductor, 
>> and
>> the impedance at this point (when tuned) should be about 50 ohms, so the
>> voltage isn't that high (350 V.?),  and the current would be about 6 
>> amps.
>> Relays for this should be a dime (well, $20) a dozen?  As a mtter of 
>> fact, I
>> see one like this would handle the job if never switched "hot" which you
>> wouldn't want to do with a rotary switch either!
>> http://www.mv.com/ipusers/lint/K1HI/RelaySpecs.pdf
>>
>> I'm also looking at compact tank coils in the literature.  How much power
>> could I expect to run with two muffin fans to cool the tubess and 
>> operating
>> CW contests?
>>
>> Thoughts?
>>
>>    -Rex-
>>
>>     Rex Lint, Consultant
>>     26 Brek Drive
>>     Merrimack, NH 03054
>>     PH:    603-860-7651
>>
>>
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> 
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