Pal 321 base tube amplifier help.

[Tinkerjim]

Hello i have a pal 321 tube amplifier base.
It has 1 6lf6 driving 3 6lf6.
It lights up
All tubes light up good
Fan runs good as well.


But it does not transmit.
Radio won't even transmit through it.
So far i have changed both big filter capacitors as well as the recifier diodes.
Some one said it could be relays.
Had problems finding right ones.
So i ordered a relay kit offline. I build the kit as instructions said.
But I'm having trouble getting it wired to the amplifier.
Any help would be appreciated.
Thanks Tinkerjim.


Fan

[443 Arizona]

first, pull the tubes and store them safely while messing with the amp.
it does appear that it may be a relay problem, but i dont think your relay kit is the answer.
your input should be present , so focus on the output,,,
tubes can light up but still be bad,,,, also, give it 10 or 20 minutes of on time to fry in any loose electrons, your just going to have to trouble shoot it all really,
some special equipment would be extremely helpful,, at that point, take it to a radio shop.

[MDYoungblood]

You would be surprised at how many of those older tube amps have been hooked up backwards and fired the relay circuit. If the relay is closed when “off” the radio should transmit through the relay to the antenna jack. If the relay is clicking when it senses wattage try switching tubes around, if one is bad it would most likely be the driver tube.
Wish I could be more help.

3’s

Greg

[Tinkerjim]

Thanks for the response.
The relay was not clicking.
No power getting through.
Not even the radio transmit. Nothing.
The original relay board had 2 relays
2 pins on bottom. 6 pins on top.
I'm trying to install a relay kit i bought online. This relay board has only 1 large relay.. Any ideas on what I'm doing wrong would be appreciated.. Thanks Jimmy..

[warlock35po]

Hello. I have seen many 20LF6 sweep tubes light up really good and still test next to nothing on a Mutual Conductance tester.Hope that is not the problem .At a guess I would say a new old stock 20LF6 could easily be better than a 100 bucks each,plus insured shipping, good luck.Regards, warlock35po

[Monk]

Hi,

I know it has been over a year when you started this thread and don't know if you ever got the 321 going.
Have you gone to CBtricks and downloaded the schematic?
From what you said about the tubes (6lf6 not 20lf6) lighting up that means the 12 volt winding on the transformer is working. There are four 6 volt tubes in this amp. The tubes are paired up across the 12 volt line like batteries in a flash light. There are two 6 volt filament pins on each tube that take 6 volts. So with two 6 volt tubes you have a total of 4 pins which 1 pin of each tube is tied to 1 pin of the other tube. Then, the 12 volts is fed to the two pins not connected thereby giving 6 volts to each tube. This amp also came with 8950 tubes which take 12 volts to light them up so the pairing was not needed when using 8950 tubes.
From what you also said about no power going through the amp even when not keyed up says to me relay problem, dirty or worn out contacts in the relay. There is another thing a much less common one and that is a bad solder joint/loose connection.
Warning, never work on an amp when plugged in. After turned off and unplugged short a screwdriver to the tops of the tubes and ground, and underneath short to ground the 450volt electrolytic capacitors.
The amp not keying up (clicking) can be a few things:
The keying transistor needs replaced.
The 12 volt DC diodes need replacing or the 25volt 250uF capacitor is shorted to ground.
Much less common is the reverse diode on each relay is shorted or the coil in the relay is open. You can test the relays without 120 volts to the amplifier. Use you power supply that you have your radio on, or even a 12volt DC wall wart transformer. Hook the negative lead to ground/the metal chassis and the positive lead to the 25 volt 250uF capacitor plus side(the rubber/plastic end not the full metal end). Take another wire with one end to ground and tap on one of the leads on the relay that has the diode across it with the other end. If you have a volt meter there should be + 12 on both diode leads on the relay. The keying transistor shorts one lead to ground to make the relay do it's job. If the relay does not click tap the other end of the diode.
Part two coming up in a couple of days.

Monk---out

[warlock35po]

Thanks Monk, Ian sure a bunch of people will get a lot knowledge as for me because of poor health all I can do is turn them on or off. Have a happy Christmas and New Year.Regards Warlock35po