Johnson Courier Amp Power Supply Question.

[w3kbs]

Hello everyone. I am in the process of restoring a Johnson Courier Amp.
I replaced all the Electrolytic Caps and all the bias supply components. The bleeder resistors look ok.
When I try and put the power to the set it shorts and blows a fuse. It also took out the 866a in the back of the set. I have no way of testing the rectifier tubes. I also tried the 3b28 tubes and it still blows a fuse. Also, I have no way of testing the rectifier tube 3b28.
Was wondering if someone else has had this problem?
I ran the set without the rectifier tubes and all is fine when I apply high voltage.
Before I replace the 866a with new or almost new 3b28s has anyone else experienced this problem and found what the cause was?
Thanks in advance.

Bill w3kbs

[KA2DZT]

With the 866s out of the sockets how are you applying HV??  What HV are you referring to??

[Pete, WA2CWA]

With the AC disconnected:
I would remove both final tubes.
Next, measure the resistance from the cold end of L5 to ground. You should see 50K or more.
If not, cap C12 might be shorted.
Check the electrolytics in the HV line to make sure they were all installed in the right direction.
Page 30 of manual gives typical resistance values for the transformers and choke. Need to determine if any of the windings are shorted or shorted to ground.
When you had the 866A's and 3B28's in, were the filaments lit? It's possible, they could be bad even if the filaments light.
BE CAREFUL!! The unloaded AC voltage across the the secondary of T1, the HV plate transformer, is 3600 volts.

[w3kbs]

Hi everyone. Let me run the described tests and I will get back to all of you.
Tnx sooo much for the help.

Bill
W3kbs

[W4AMV]

Hi Bill.

The bleeder resistors look ok.

Don't make the mistake I made. Don't have a schematic of the Courier in front but if it uses equalization R's across the HV caps and they look good.... That's not good enough! Measure them to be sure. Lift one end off each cap.

73' Alan