I replaced all the capacitors on the power supply board and reinstalled it.
I disconnected the primary to the HV transformer so I could connect it to a
variac while the rectifier tubes had full filament voltage applied. I turned
on the amp and let it warm up. With my multimeter on the HV supply, I
brought up the variac until the meter read 1000vdc (the meter's limit). The
input ACV was about 50v. That seemed about right for 2000+vdc at 120vac
input. I powered everything down, reconnected the HV transformer, and went
through the power up procedure again. The HV choke is buzzy. Power down
again. Install tubes. Power up filaments. Turn on HV. Loud heavy
electric-chair buzzing and then the fuse blew. I don't have a supply of 12a
buss fuses so I ordered a bunch from Digikey and they just arrived. I
removed one of the tubes and powered up. With HV on, still good. When I
tried the other tube by itself, the fuse immediately blew. I guess the tube
is shorted. I googled a 7094 tube and found the price of one tube is more
than what I paid for the whole amp. I removed the bad tube and put back the
good one and drove the HT-41 with a Drake 2-NT. Seemed to work fine, though
with less than 75w drive, I read about 200w out. I guess I'm left with a
one-legged amp!
Tom n7tm
From: "David C. Hallam" <dhallam@rapidsys.com>
Reply-To: <dhallam@rapidsys.com>
To: "Tom Taylor" <tomastaylor@hotmail.com>,<amps@contesting.com>
Subject: RE: [Amps] Halli HT-41 amp
Date: Tue, 27 Mar 2007 13:30:51 -0400
Install the capacitors you have. You will never know the difference. As
far as 120VAC line goes, while there would be plus to have 240AVC input on
the transformer, the 7094's don't run enough power to really need 240AVC.
David
KC2JD/4
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]On
> Behalf Of Tom Taylor
> Sent: Tuesday, March 27, 2007 12:45 PM
> To: amps@contesting.com
> Subject: [Amps] Halli HT-41 amp
>
>
> A few weeks ago I bought a very good condition Hallicrafters
> HT-41 amp at a
> local hamfest for a hundred dollars. The amp is now the heaviest piece
of
> gear I own; just shy of a hundred pounds. I struggled carrying that
thing
> the few blocks from the hamfest to parking lot. The HV transformer looks
> like an old-style TV power transformer, but super-sized.
> Surprisingly, it's
> 120vac only. The amp is clean inside above and below the chassis
> and there's
> no evidence of anyone monkeying around with the wiring.
>
> The first thing I'd like to do is replace the 40 year old HV power
supply
> caps with fresh ones. The existing supply has six 100mfd 450vdc
> caps wired
> in series for a total of about 17mfd capacitance. The power supply is a
> choke-input design. In my junkbox I've got plenty of new 120mfd 450vdc
> capacitors. They're about a fifth of the volume as the original
> ones. This
> will give me 20 mfd total capacitance. With this choke-input supply, is
> there much benefit (and it has to outweigh the time and cost of ordering
> larger capacitors that I don't have) to installing larger capacitors?
>
> Thanks,
> Tom N7TM
>
> _________________________________________________________________
> Exercise your brain! Try Flexicon.
> http://games.msn.com/en/flexicon/default.htm?icid=flexicon_hmemail
taglinemarch07
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