[Hallicrafters] HT-33A PL-172A Tube substitute modification

Mon Nov 7 15:32:42 EST 2011

OT -

Carl,

You seem to be quite knowable about a wide variety of rigs and different 
types of equipment. Perhaps you can give me some ideas on a James B. Lansing 
model 4320 Studio Monitor.

This one was actually used for some years in the infamous RCA Nashville 
Studio B studio as one of two such monitors.

I would like to use it as my center channel speaker with my H.H. Scott 
LK-72B amplifier and H.H. Scott LT-110 FM/FM stereo multiplex tuner. The 
H.H. Scott 'B' model has the center channel, the others do not.

It is a mix of left+right and fed off the rear of the chassis via a mono RCA 
female jack. It does require an external amplifier to power the center 
channel. However, the H.H. Scott LK-72B does control the external amplifier, 
that is, after the initial settings are set on the external amp.

I am using a pair of Paradigm Monitor 9S for the mains.

The amplifier I would like to use to power the center channel is a vintage 
1974 Sony TA-1144 solid state amplifier. It delivers 35 watts continuous RMS 
per channel. I would set the amp up for mono operation, as the Sony TA-1144 
has a front panel control that allows the user to have the output in; 
stereo, left/right reverse stereo, right+left mono etc.

I think the output impedence on the solid state TA-1144 is 4 ohms, and the 
JBL 4320 is 16 ohms. The LK-72B is selectable, either 4 ohms or 8 ohms.

What is the best way to configure this Carl? Thank you sir.

----- Original Message ----- 
From: "Carl" <km1h at jeremy.mv.com>
To: <w7apm at mtaonline.net>; "jack m" <oldvette at hotmail.com>
Cc: <hallicrafters at mailman.qth.net>
Sent: Saturday, November 05, 2011 7:20 PM
Subject: Re: [Hallicrafters] HT-33A PL-172A Tube substitute modification

>I wonder how hard it would be to adapt a 4CX1000A/1500B?
> Tubes are readily available NOS military surplus and sockets at a 
> resonable
> cost show up at times.
> The FU-728F will also work in the 1000A/1500B socket with a simple mod.
>
> The 4CX-1500A is another candidate if the PS area is modified to allow a 
> big
> filament transformer. The 5CX1500A/B and sockets also show up at times.
>
> Ive also heard a few on the air with 8877's.
>
> Carl
> KM1H
>
>
>
> ----- Original Message ----- 
> From: <w7apm at mtaonline.net>
> To: "jack m" <oldvette at hotmail.com>
> Cc: <hallicrafters at mailman.qth.net>
> Sent: Saturday, November 05, 2011 7:38 PM
> Subject: Re: [Hallicrafters] HT-33A PL-172A Tube substitute modification
>
>
>> Jack,
>>
>> I suppose you know about the 8295A Eimac? Direct replacement and ceramic
>> instead of glass. I was given a homebrew PL-172 amp at one time from a
>> elmer and got it on the air. (He was scared of it) It worked well and at
>> 2,700 watts out I quit turning up the drive although the amp was willing!
>> Anyway, I got 4-5 PL-172 tubes with it and only had one fail when I
>> applied the High Voltage. I got impatient and didn't "Getter" it long
>> enough. I still have one of the tubes and thinking maybe some day I will
>> find a use for it. There is an arcticle in the March 1958 QST on
>> homebrewing with the PL-172...
>>
>> --...  ...--
>> Marty/KL7AM
>>
>> --- oldvette at hotmail.com wrote:
>>
>> From: jack m <oldvette at hotmail.com>
>> To: <hallicrafters at mailman.qth.net>
>> Subject: [Hallicrafters] HT-33A PL-172A Tube substitute modification
>> Date: Sat, 5 Nov 2011 21:56:35 +0000
>>
>>
>> Hello group,
>>
>> For 5 years, I have patiently searched for a useable PL-172A tube for my
>> HT-33A amp.  3 EBay used PL-172A "wins" have been - well, you guessed
>> right.
>>
>> The PL-172 market is getting worse!  In favor of a winter boat-anchor
>> project this year, I've decided to give up looking.
>>
>> As much as I would like to keep this near-mint amp original, the desire 
>> to
>> actually use it with my HT-32A has won out.  I was discussing this on the
>> air this past week, and the ham on the other end recalled another ham who
>> had converted his HT-33A rig to run one of the ceramic tubes, but he was
>> not a boat anchor afficianado and did not have any details.  He did 
>> recall
>> that ham as stating that the socket and chimney/air cooling system, as
>> well as the various voltage supplies, were not all that difficult or
>> complicated to modify and adapt to the HT-33A chassis or design power
>> supplies.
>>
>> Is there anyone out there who knows of this mod, and where could I find
>> the details?  As a "purist", I would prefer to be able to de-modify it in
>> case the PL-172 market improves sometime in the future.
>>
>> Thanks
>>
>> Jack W3RU
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