Posts: 81
Threads: 24
Joined: Aug 2018
City: LAVERN-SUBIRATS
State, Province, Country: ESPAÑA
Hello,
Some time ago I restored an Atwater Kent, model 82. I changed all the capacitors, non-tolerance resistors, et ...
There is a problem. When I turn on the radio the volume is practically at maximum. After a few seconds the volume drops and works normally. I've gone through everything, and nothing.
I do not understand.....!
I will appreciate if someone tells me that it can happen.
Thanks.
Posts: 4,639
Threads: 51
Joined: Sep 2008
City: Sandwick, BC, CA
Not that it is related you your problem but I hope that you replaced the original wiring on the power transformer, if it still has the original transformer?
With regard to the volume level, where is the control set when this happens? I'm wondering whether it is a case of rather then the volume going up, and then dropping to a normal level, whether it might be that the level might be that the volume control is set high, and the gain is dropping after the set warms up?
Posts: 81
Threads: 24
Joined: Aug 2018
City: LAVERN-SUBIRATS
State, Province, Country: ESPAÑA
Posts: 2,118
Threads: 112
Joined: Jun 2010
City: Medford OR (OR what?)
Yes, you have to replace the original rubber insulated wire IN the AK transformers. I have never had one fail after doing this. And, rewiring an AK trans is easy since no splice is required.
Russ
"I just might turn into smoke, but I feel fine"
http://www.russoldradios.com/
Posts: 3,122
Threads: 57
Joined: Apr 2011
City: Lexington, KY
When this happens if you just turn the volume control a hair one way or the other does it go back to normal? That volume control (if original) is about 90 years old now so it might need an occasional, or maybe initial cleaning.
You might also want to clean the pins on your tubes (a very fine emery cloth works well for that). Maybe lightly tap on various tubes with a non-metallic object (wooden chopstick maybe) when this is happening. You might want to substitute in a different set of known good tubes.
I also like to check and make sure the tube sockets are all tight and then I clean them with some contact cleaner on these little brushes I got from Harbor Freight for airbrushes:
https://www.harborfreight.com/airbrush-c...68155.html
I'd also suspect any original resistors that you didn't replace and also look for any cold or suspect solder joints, both old and new. An intermittent problem that only happens for a few seconds can be hard to find.
John KK4ZLF
Lexington, KY
"illegitimis non carborundum"
Posts: 900
Threads: 8
Joined: Jul 2020
City: Greenlawn
State, Province, Country: NY
Sorry, I know that this is 4 months late but here goes:
The 82 schematic is interesting to say the least. Look into the 24A that is referred as the CONT (Control?) tube, This may be an AVC circuit. The volume control is part of a resistor "Ladder" Voltage divider for various B voltage, Check for voltage variation at either end leg of the volume control and all along the "ladder" for changes in voltage. Replace questionable resistors and caps. Check for changes at the wiper. However, the wiper voltage may change as the "Control" Tube warms up. Read on.
The volume control varies the cathode bias of the "Control" tube, which varies grid bias on the 1st detector (Mixer) and the IF Amp. Based on where on the voltage divider the cathodes of the IF and Mixer and the plate of the Control Tube are, the plate of the Control tube is negative with respect to the cathode. The more current that passes through the tube the more negative the plate gets in relationship to the Mixer and IF Cathodes, making the grids of these tubes more negative. Cathode voltage of the 2nd detector controls the grid voltage of the Control Tube, therefore AVC is obtained. As the current of the tube goes up, the bias on the mixer and IF amp is increased. Could be that slow warmup of that tube is the issue. Swap with the 2nd detector, or dig up a 24A from somewhere else. The 35 is a somewhat similar tube but is a remote cutoff (Super Control) tetrode, as opposed to the 24A which is the standard sharp cutoff tetrode tube.
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
Best Regards,
MrFixr55
(This post was last modified: 04-04-2022, 10:31 PM by MrFixr55.)
Posts: 1,472
Threads: 89
Joined: May 2008
City: Omak
State, Province, Country: WA
Hello Eliot Ness ,
what great idea far as those cleaning brushes I will pick some up!
Well, Ferran I look forward to your restoration of this set because this last year I bought myself an Atwater Kent Model 89 and I look forward to restoring it !
Sincerely Richard
Posts: 81
Threads: 24
Joined: Aug 2018
City: LAVERN-SUBIRATS
State, Province, Country: ESPAÑA
Hello,
I've changed the tubes, to no avail. I'll check the potentiometer. I have noticed that it is not the original. The former owner changed it. When I have time I'll look at it.
Thanks for the observations.
Posts: 900
Threads: 8
Joined: Jul 2020
City: Greenlawn
State, Province, Country: NY
Hi Ferran,
Note that the volume control is supposed to be only 550 Ohm. I don't know how many watts the volume control should be able to handle, but the more, the better. The control is part of a "voltage divider". The total resistance of this string is is about 30,000 Ohm. The percentage of this string that is the resistance of the volume control is only 1.8% of the total resistance and 1.8% of the approximately 250V across this voltage divider. The voltages on the tube are very small, being 16V for the plate, 8V for the grid and 4V for the Cathode. However, these readings were made with a 1000 Ohm / Volt meter instead of one of the modern supersensitive DVMs.
The point here is any change in resistance as these resistors and the 80,000 plate load resistor heat up will possibly cause the issue that you are having. In other words, consider changing all of the "bleeder resistors", the volume control and the 800,000 Plate Load Resistor for the Control Tube. In addition, change all of the capacitors in the radio.
Good luck, I hope that this helps.
Best Regards,
John "MrFixr55"
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
Best Regards,
MrFixr55
(This post was last modified: 04-08-2022, 04:48 PM by MrFixr55.)
Posts: 81
Threads: 24
Joined: Aug 2018
City: LAVERN-SUBIRATS
State, Province, Country: ESPAÑA
It could be John. I will keep you informed.
Regards,
Ferran
Posts: 81
Threads: 24
Joined: Aug 2018
City: LAVERN-SUBIRATS
State, Province, Country: ESPAÑA
I have already seen the error !!!!!
You were right, John. The fault was related to the control tube circuit. The potentiometer is correct: 550 ohms. The fault was in the 670 ohm resistor. It read 1,000 ohms. Totally out of tolerance. I had not noticed.
The radio works perfectly !!!!
Thanks for the help.
Regards,
Ferran
Users browsing this thread: 1 Guest(s)
|
Recent Posts
|
Cannot Adjust an IF Transformer’s cores
|
It works! I received the PCBs this morning in the mail, and put everything together. I reused the base from the original...jrblasde — 04:32 PM |
PT-6 antenna connections
|
I seem to have lost my way on this PT-6.
I see the antenna aerial transformer schematic - I’m reading pins 1 through ...bridkarl — 12:30 PM |
40-150 General questions
|
Good thing you're a good electrician ... the pictures show a lot of rewiring in your future! Take care and BE HEALTHY!...GarySP — 11:52 AM |
40-150 General questions
|
I think RobB has it right. It is a part number and looks like its stamped on the chassis and that wasn't something you ...klondike98 — 11:41 AM |
40-150 General questions
|
It's most likely a part number. Most of Philco part numbers are in that format. I looked at the parts list for this mode...RodB — 08:10 AM |
40-150 General questions
|
Hi Kevin,
No, I don't but I like your Quote about being a good electrician. The way I look at it is "The fact ...MrFixr55 — 08:06 AM |
Philco 38-7 Speaker
|
7K should be fine. While not a perfect match (This transformer is meant for 6V6 tubes), Antique Electronic Supply (AES)...MrFixr55 — 08:03 AM |
40-150 General questions
|
I discovered a stamp on the underside of the breadboard on my Philco 40-150. It is"56-1417' in black ink with numbe...Kevin_D — 07:14 AM |
Philco 38-7 Speaker
|
FYI the Impedance of the HR20 (the one I have) secondary of the audio transformer is 5 ohms. The 38-7XX speaker is suppo...tludka — 04:22 PM |
Philco 38-7 Speaker
|
Yeah, don't use the transformer currently on the H-20 (Dopf, I thought "H20, is that new technology, a speaker usin...MrFixr55 — 03:51 PM |
Who's Online
|
There are currently 2305 online users. [Complete List] » 1 Member(s) | 2304 Guest(s)
|
|
|
![>](https://philcoradio.com/phorum/images/bootbb/asb/right_arrow.png)
|