Thank you to all who replied. The diodes have been sourced and purchased.

73,
Jeff
W8KZW

Hi Jeff,

You can find the NTE506's on eBay,? 20 for $20

Or



Otherwise, if it were me replacing diodes in my PS-150-120,? since I have a box of 1N4007's, ? I would double them up (2-per leg in the bridge) if it bothered me to use single 1000V diodes 1 per leg.
--
73/Rick
W4XA
__________________________________
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FWIW, I have a couple of hard copy "Radio's Master" catalogues.
Others are on the worldradiohistory.org site. The ones I have are 1947
and 1953. The early one does not list any molded paper caps, the 1953
edition shows Sprague Telecap, called Black Beauty in quotes but without
RMA code striping. These are described as "dry process" caps with the
same qualities as oil filled ones. In any case, I believe these are the
replacements for the Black Beauty caps. I am too lazy to look at the
on-line catalogues but, from memory, it seems to me that BB was used as
a trademark about 1950.
The 1953 catalog also shows Sprague Vitamin-Q caps.
Some older Hewlett-Packard instruments, like early 400D and similar,
have molded sprague caps with RMA coding on them. These do not seem to
have failed and don't show the mechanical disintegration of the caps in
the Hammarlund receivers. I don't know if they are the same caps or not.
The signal corps issued modification work orders to replace all
paper caps in the SP-600 about the mid 1950's, I don't know the exact
date. The caps were replaced with disc ceramic types.
The Black Beauty caps were advertised as "deluxe quality at no
higher price" for use in locations with high heat. Telecaps were
advertised for similar applications especially, as the name implies, in
television sets. Other manufacturers made similar molded caps, for
instance, Cornell-Dublier made Blue Cubs. Paper caps of all types have
limited lives but the Black Beauty seems to have had a special problem.

--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

Paul
There is a tiny bit of backlash but not bad at all. The piano string on this one is in really good shape. I am thankful it did not need replacing. I do need to align the dials properly. They were off a small amount when I began this project. Good thing thats an easy task now that I have longer spline tools. Now to finish painting the cabinet and reassemble.?

indispensable, is BASS FIDDLE ROSIN. I treat those pesky dial cords with
it, and they NEVER slip thereafter.? Violin and Cello are too hard a
compound... use the BASS stuff.

Tom - W?EAJ

Dan:

?I would check the following capacitors? C4, C6 , C8. These all appear to be bypass capacitors going from B+ to ground. I am just thinking if they were leaky or shorted they might cause the problems you are having.

Just my 2 cents worth, and I hope it helps.


Howard, N9KTW

Looking to purchase subject diode for my power supply. Maybe 1 or 2 extra just to have around.

Please reach me off list.

Thanks, & 73,
Jeff
W8KZW

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After much patience, the SX100 is working nicely. Very pleased with the results. Pays to not rush. Thank you all for the pointers. Still working on final tweaks, but it’s playing now where before, it was nothing.

On Fri, Apr 26, 2024 at 03:35 PM, Richard Knoppow wrote:

I have lost track here. Have you just shorted the mic connector to
see what happens? If you have does the noise continue?

Yes, that was an early test.? Yes, the noise was still there.? I previously had biased off the first mic stage and the noise disappeared, so I concluded that it wasn't coming from the audio strip.? But, tonight I just removed the mic line at the grid of the second mic amp and the noise was still there.? Not sure why it wasn't there when the first stage was biased off.? Maybe I made an error.? At any rate, it now appears that the noise could be coming from the audio strip at the third mic amp or the audio modulator.? If I pull V5, the 12AT7 audio modulator, the noise is gone.? Next will examine the phase shift network between the third mic amp and the audio modulator.? I know the audio outputs from V5 are equal as I previously had a bad bypass cap in the output and one channel was way down.??

Flyd

On Fri, Apr 26, 2024 at 03:31 PM, waltcates wrote:

How and where are you sampling when you see the noise.

The noise if being observed (visual and audible) on an external transceiver spectrum scope.? The signal is being sampled at a sampling port on the dummy load and is applied to the monitoring transceiver at a receive-only antenna port.

Floyd

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I have lost track here. Have you just shorted the mic connector to
see what happens? If you have does the noise continue?

--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

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Well, the AALC idea didn't pan out.? I disconnected one end of the diodes and also removed the plate supply from the AALC amplifier stage.? No change whatever.? Also played with the mic? connector lead and there was no difference in the noise level or pattern with both ends of the cable grounded vs. just one end.

Floyd

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Thank you sir?

--
Tony Lunsford?

On Tue, Apr 23, 2024 at 10:09 PM, Paul Christensen wrote:

I don't own an HT-44 but looking at the manual, it uses AALC like some other Hallicrafters gear.? Possibly part of what you're experiencing is a low-threshold AALC.? Temporarily disabling it may help in localizing the noise source. From the manual:

Interesting idea - thanks, Paul.? Will look into that.

73, Floyd - K8AC

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