Tom,
Tubes are a problem with the old Hallicrafters amps, not cheap. Have you
searched for a something similar in a more available tube for a conversion?
David
KC2JD/4
> -----Original Message-----
> From: Tom Taylor [mailto:tomastaylor@hotmail.com]
> Sent: Friday, March 30, 2007 10:30 PM
> To: dhallam@rapidsys.com; amps@contesting.com
> Subject: RE: [Amps] Halli HT-41 amp
>
>
> 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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