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 on: Yesterday at 06:21:29 PM 
Started by WZ8J - Last post by N1BCG
300 Volts approximately. Mine shows a bit more because line voltage is higher now than in the 1950s. Anything from 300-340 should be ok.

 on: Yesterday at 05:48:17 PM 
Started by WZ8J - Last post by WZ8J
what should the LVb+ be 300V?

 on: Yesterday at 05:00:44 PM 
Started by KC3GMQ - Last post by K6JEK
Mine is paired with a Heath AR-3 and the QF-1 Q multiplier. They look fine together but the AT-1 gets out better than the AR-3 hears. When I was a novice, the people I talked with who had AT-1s had something better but still cheap as the receiver. So when I fire up the AT-1, unless conditions are superb, I use my novice receiver, a National NC-125 which is a huge improvement over the AR-3, from the right era and still cheap. Besides, the built in Select-O-Ject is fun to use.

Here's the NC-125 in fine company:

 on: Yesterday at 03:48:49 PM 
Started by WZ8J - Last post by N1BCG
You might be fine. Put your voltmeter on either + lead of that cap and to the chassis to monitor LVB+ as you bring up the Valiant on the variac.

 on: Yesterday at 03:35:42 PM 
Started by WZ8J - Last post by WZ8J
You mean all might not be lost?
I do have replacements for the C98 dual cap.
I'm going to check the pin out for the 5V4 and check for shorted tube with my VOM

 on: Yesterday at 02:49:16 PM 
Started by WZ8J - Last post by N1BCG
Don't necessarily be concerned about the mod xfrmr resistances. Those windings have relatively low D.C. Resistances. So far, it just sounds like a cap failure.

Got replacements for both? A shorted 5V4 could have done that.

Also, only use a stereo (3 conductor) plug and keep the tip and ring leads well separated. One is for low voltage audio, the other has -180 volts on it for keying when connected to ground/shield.

 on: Yesterday at 02:35:43 PM 
Started by WZ8J - Last post by WZ8J
I think you're on the right track Clark. The studio mic has no ptt.
The jack is wired to the audio pot and to the hot side of SW-8
The smoke looks like it came from arcing at C98 (Electrolytic cap on the 5V4 to ground. C98 came unsoldered from the ground lug.
The leads from T-3 mod transformer are all connected to a terminal strip.
I measured resistance from each lead to each of the others and found them all shorted.

 on: Yesterday at 01:37:48 PM 
Started by WZ8J - Last post by KA2DZT
It happened when I plugged it in. SW8 still on PTT.
I have a variac, won't that accomplish the same thing as the 150W bulb?

Not exactly,  the light bulb prevents a heavy short from damaging the xfmrs and other parts.  A Variac doesn't do anything to prevent damage from shorts.


 on: Yesterday at 01:33:06 PM 
Started by WZ8J - Last post by N1BCG
Trying to piece this together... so the transmitter was set for "AM", on standby, and just needed to be keyed? Then the mic was plugged in and BANG!  Right?

Is that added jack definitely for a microphone and does it include a contact for keying? If so, what might have happened is the -180 Volts used for keying got into the audio input circuit and that would have sent a thunderous pulse through the modulator. Is the studio mic wired with a PTT circuit? Usually those mics are balanced 600 Ohms where two leads are for audio and the third is grounded. I'd be surprised if it were wired for PTT if it had a 1/4" plug.

Where did the smoke rise from?  I'd trace the leads from that added jack to confirm its purpose. Variacs are very handy, especially if they have a current meter.

 on: Yesterday at 01:24:25 PM 
Started by K5WTX - Last post by K5WTX
I am looking for the two BCB coils (E and F) for an HRO-7.  My receiver is a HRO-7R  which is the black crackle painted rack mount version, however I can use coil for the HRO-7 table model (grey).  I have a grey A, B, and C coil that I would be willing to trade.  Thanks for reading my post. 

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