Admiral Imperial 330 Chassis 16ASIC - Videokarma.org TV - Video

RedDodge1968 · #1 12-23-2011, 10:12 PM

Hello fellow vintage electronics enthusiasts. I am new here to the site, and am still in the learning process of vintage electronics. I have an Admiral Imperial 330 console I am having some trouble with. I lost the picture some years ago after attempting to replace the electrolytic capacitors. The TV would not maintain a horizontal lock, I was constantly having to re adjust. I have pulled the TV back out to work on it again, I have completed a complete recap, and replaced two open power resistors, as well as a defective carbon resistor. I have a good picture now, but there is a HUM in the speaker that I think I am seeing corresponding noise in the picture, but I am not sure on that. Does anyone out there have any suggestions? I have double checked all of my electrolytic capacitors, wiring, and connections, and cross referenced them with the SAMS fact, what am I missing? Thanks in advance for any help. Kevin

ctc17 · #2 12-23-2011, 10:45 PM

hum or buzz? Is the hum there with the volume down? Or is it a buzz that happens mostly when text is displayed in the picture?

AC line hum would be from most likely something with the filter caps, check them again, then something with the rectifiers or a tube with a heater to cathode leak.

RedDodge1968 · #3 12-24-2011, 08:25 AM

It is a hum, you do hear some noise changes depending on the picture being shown, but my audio is distorted as well, the sound actually resembles that of an old radio with bad filters, but I have double checked them, as well as re replacing all of the NOS capacitors I put in there years ago with new ones. The old rectifiers have been replaced with diodes. I double checked all of the tubes again, I had already replaced several tubes, I did find another that develops cathode to grid leakage after a long warm up 12DQ6B, but it is not the source of my trouble either.

bgadow · #4 12-24-2011, 09:40 PM

I would make sure there weren't some misrouted wires; perhaps the speaker wire or maybe the line from the tuner is picking up intereference? If it is a parallel chassis I think I would just start pulling some select tubes one by one and see if any will make the noise go away; not so easy with a series string. Have you cleaned the tuner? Just some ideas.

RedDodge1968 · #5 12-25-2011, 09:19 AM

This is a series wired set, I have retraced all my connections, over and over, double checked all of my solder joints as well. I have made a little progress though, there is a 40 MFD electrolytic that feeds ground side into a pot labeled "noise gate" the + side feeds into the audio out put transformer. When this is disconnected the noise decreases (however the sound is still distorted, and hum is still present) and the picture gets darker, and clarifies more.

I have tried different configurations with the capacitor to no avail. I believe my problem lies within this circuit, but I believe it may be something its not getting from elsewhere.

Someone answer me this. I am unable to test the CRT at this time, is it possible for my noise issues to come from shorts or leakage within the CRT?

ctc17 · #6 12-25-2011, 11:05 PM

I dont see how the crt could cause it. If it had selenium rectifiers I think you need to add a series dropping resistor. The new diodes are much more efficient that the old stacked diodes and you could have B+ thats way to high.
Most old sets seem to buzz with a bit with modern programming but not really hum. Does it have a filter choke? could it be shorted?

What is the Sams number?

RedDodge1968 · #7 12-26-2011, 09:02 AM

I thought of that as well, I tried a resistor inline with the diodes and it made no change to the sound at all. It does have a few chokes scattered around, it has a line choke in the power cord coming into the set. I went through every resistor pulling them off of the board and double checking their value, I replaced anything that was not within 5%, and that changed nothing. SAMS Set 438 Folder 1

Reece · #8 12-26-2011, 10:07 AM

Can you tell by tracing if hum is in the audio section or before it? Sometimes h/k short in output tube. Check all chassis grounds that depend on rivets: they can oxidize and cause hum.

dieseljeep · #9 12-26-2011, 10:47 AM

Quote:

Originally Posted by Reece

Can you tell by tracing if hum is in the audio section or before it? Sometimes h/k short in output tube. Check all chassis grounds that depend on rivets: they can oxidize and cause hum.

I was just going to post that. IIRC, those PC boards are held with screws.

RedDodge1968 · #10 12-26-2011, 12:41 PM

THE TV IS FIXED!!!!!!!!! I am ashamed to say it was the audio tube all along. I had bought a new tube for this (12C5) and as luck would have it, this new tube produced the exact same symptoms as the original. I used a 2nd tube tester for a second opinion of the three tubes I had, in my box of used tubes I had 1-12C5 that showed an excessive leakage but no shorts. This tube fixed the TV, so some new 12C5 tubes are on order. Thank you all for your help, and opinion's, you have kept me motivated to search for this problem, see this TV in operation on You Tube channel RedDodge1968, I will soon upload a video of the TV reassembled. Don't mistake this TV for my other Admiral Super Cascode, I have two Admiral sets, the other is next in line for an electronic restoration.