I'm recapping a Truetone Model D1032A (www.nostalgiaair.org/Resources/645/M0023645.htm). All is going well, however, I have to replace a .001 800V capacitor---all I have is a 630V...can I use this replacement voltage? I believe the answer to be no, if so, where can I purchase a 800V capacitor?

Thanks for viewing this post,
Mike

That would be C29, across the primary of the output transformer. Your answer is yes, you do need at least the specified voltage there, in order to handle output voltage peaks and transients.

You don't need to find a single unit, however. A pair of .002 units (630v) in series will give you what you want, with an extra working voltage cushion.

Larry

Thanks Larry---I'll do it.

Mike

Always glad to oblige. Good luck on your project.

Larry

A .001 1KV or 3Kv disc is pennies at Mouser or I can mail you one

Carl

These often short out, as the peak voltage can be horrendous if the output tube goes to cutoff on a thundercrash or a switching transient when you move the bandswitch. Use a 1KV cap at least.

I would go with the 3KV disc because it is almost bullet proof. I've seen a lot of people recommending two series capacitors in place of one capacitor. The series capacitors work, but depending on their tolerance the voltage drop across each capacitor is not equal. Be wary of the two cap solution if the voltage margin is close. Two 250 volt caps in series is going to fail at 500 volt working voltage.

I replaced the electolytics (surface mount can). Disconnecting and leaving the can, I used the chassis for grounding the new electrolytics (drilling and soldering the negative ends). I replaced all the capacitors-----at C29 I used two .002 630v in series instead of the .001 800v on the schematic. When powered up I have some problems: when using the phono jack all plays well no overheating; when switching to either am or fm the radio overheats quickly and smokes. The problem area is C-28C (I'm using a 47mf in place of the required 40mf) and R-28 (820 2W). When switching from phono to radio bands there is an abrupt click then heat and smoke. I replaced the 820 resistor with the same results. Any ideas?

http://www.nostalgiaair.org/PagesByMode ... 023645.pdf

Mike

I have cleaned up my work and replaced the electrolytics and resistors (again)------same results. It is the R-28 820 2W resistor that overheats. The voltage from the rectifier tube is around 160 to 169 volts--seems exceptable? The only thing left for me to do is drive my tractor over it---any suggestions welcomed.

Mike

Unplug the radio and put your ohmmeter on the side of the 820 ohm resistor that's away from the rectifier tube.

It should measure many, many K ohms. It's probably measuring a dead short, due to C3 or C5 being shorted.

Use your ohmmeter to follow this B+ wire around and snip capacitor leads until you find out which one is shorted.

( Or what B+ wire is touching the chassis ).

Hi Mike

Cap C5 is 5000 mmf. Has it been replaced? This should be the only cap which will cause overheating of 820 ohm resistor with switch in radio position. Other points are supplied through 1K resistors. These resistors will burn first if there is a short on the other side.

+1; also be sure you do not have a short in the wiring around pin 1 of the 6ab4 or pin 5 of the 6be6

Mark

Ancient_Hacker,
Thanks for the input will be testing as you suggested.

Mike

Norm,
I changed the C5 cap (used a .005mfd) and changed C4 as well. Still get the heat, however I now get a little speaker noise before the smoke comes. I probed for any wires touching all appears clear, I want to change C3 (as Ancient_Hacker mentioned) but this is a different ceramic in fact it looks like a resistor please see attachment.

Mike

Trace along the heavy black line on your schematic, above the phono switch. Most places lead to 1K resistors. These areas should not be a problem. The 1K resistors would act as fuses and smoke first.

Could the phono - radio switch be a problem? Is this a phenolic rotary switch? They can arc over and carbonize when used on high voltage.

You may need to isolate circuits as suggested by Ancient_Hacker?

Norm,
The switch is a phenolic rotary switch. I have sprayed it (contact cleaner from Radio Shack) several times. The switch looks clean and snaps smartly into place. I'm working above the phono switch and have replaced R-2, R-14 and R-16. All were out of spec., for example R-14 was 156,000 as opposed to 100K. Both R-6 and R-9 are roughly 20% higher than the schematic....I'll work on them tomorrow. A "novice" question: can I by-pass the switch with a jumper cable to rule out the other circuts? Also, could a bum 6BE6 be the cause of the short?

Mike

Mike

Might try disconnecting and bypassing the switch contacts. They can look good and still have a path to ground. Cleaning the switch an applying power before it evaporates can cause a leakage path.

I just had a Philco with this problem. The switch was used with 250 volts. The contact shorted to chassis by phenolic burning and carbonizing. I found a way around it in Philco.

A gassy 6BE6 could cause too much current to be drawn. You can pull the tube and see what happens. You could pull other tubes connected to that heavy B+ line. It shouldn't be any circuit on the B+ line isolated with a 1 K resistor.

That difference in resistor values won't do it.

What wattage is the 820 ohm resistor? It supplied B+ to the entire radio except 6V6 plate. If rest of the radio draws over 20 ma resistor should be rated more than 1/2 watt.

Good morning Norm,

The wattage for the 820 ohm resistor is 2W----should I go 5W (if possible)?

I pulled the 6BE6 tube and the over-heating was the same---so the circuts above the switch are ok??? I pulled the 6V6 and, as you said, there was no current and no over-heating. So all indications are the switch is the problem. Can a replacement be purchased? I will pull the switch and try to clean the contacts by sanding them with 220 grit paper.

Since I didn't try the console before working on it I don't know if there was a problem before; and my work created the short. The original 2W resistor was not burned, however, I don't know how long the set was in storage/non-use. Five of the tubes needed replacement as well as the recapping.

Thanks,
Mike

Mike

A 2 watt resistor is plenty large.

Pulling 6BE6 eliminates part of the circuit. There is a 6AB4 still directly connected to the line but don't think it could cause a 820 ohm 2 watt resistor to burn.

Now for the unusual part. Why does pulling 6V6 cause the resistor not to overheat? Could the resistor be overheating regardless of the switch being in phono or radio position? If that's the case output transformer may be open? Does pin #3 on the 6V6 have voltage? If not the screen, pin #4, will draw high current. This could cause the resistor to burn.

If it is the switch not a contact problem but rather insulation around the contacts. I would check pin #3 of the 6V6 first now that you found the resistor doesn't overheat with that tube pulled.

Norm,
I gave you wrong information: the 820 ohm resistor doesn't overheat only when in the phono position. When I switch to a radio selection (with 6V6 out) there is a pop at the switch and I turn the system off immediately. 6V6 in Pin #3 has voltage---175 (phono) 109 (radio). Pin #4 184 (phono) 27 (radio). Quite a difference on pin #4.

Mike