Antique Radio Repair part4! RCA 810K

Revisited on Jan 2010. The field coil is running maybe too hot. I am thinking I need to check the B+ voltage. And the plate voltages of the 6F6 audio output tubes. This radio has a new output transformer and I never checked the B+ volatage and tube plate volatages like I did in the RCA 262. Well, it's a learning experience folks!
After I checked the voltages at line voltage of 124 Volts. I found 396 Volts on plates of the 6F6 output tubes. This is a little high. RCA says 365 Volts @ 115 input volts. I think I need to lower the input voltage. I might use a dropping resistor or a bucking ttansformer. I did install a current inrush limiter and the B+ dropped to 387 volts. Power transformer and field coil still run sorta hot, circuitry looks good. I think it's just the 124 input volts being at the upper limit of the radio's design. Last year I measured the line voltage and it was 118 volts. the power company did extensive work inthe neighborhood, so maybe that why the input voltahe is now higher at 124 Volts. I'll just reduce the input voltage somewhat to around 115 volts and that should fix things.


RCA 810K installed in cabinet. Works about 90 percent of the way! Here's another tip. Don't try to clean radio dials with anything. A lot of the inks for the numbers are water soluble. Maybe just blow dust off with air? : antque radios contain hazardous and potentially LETHAL voltages. So when you have the chassis out, please read up on safety procedures!

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[smeezekitty]

@Lockemeister

The B+ is around 305v.

[Lockemeister]

@smeezekitty OK, now it get complicated

yoou need to google the words 42 tube data. The 42 tube is the same as a 6F6. You might could try 6F6 tube data too. Is this s single tube or push pull Amp with 2 tubes? The plate voltage is different for single verses push pull. You need to know the grid volteges too. If it's to ohard to do don't do it, be safe not sorry. Keep one hand in your pocket. If you are unsure have a professional do it.

[Lockemeister]

@smeezekitty i'll send you a link to a 42 and also a 6F6 tube data sheets. The single tube amp plate is like 250 volts and the push pull is around 350 volts. Some types of 6F6 push pull is 375 volts for the plate. To be sure you need to check the grid volts too. But if you are unsure leave it to the professionals. I ALWAYS keep one hand in my pocket when probing. These 6F6 tubes do run very hot when in normal operation.

[Lockemeister]

@smeezekitty you also need to find the schematic information for your model number. Try nostalgiaair. org

[smeezekitty]

Our voltage never gets runs 118v-120v, no higher so i don't think thats the problem.

Also the power transformer is very cold, maybe yours has some shorted turns?

[Lockemeister]

@smeezekitty I ended up lowering the input voltage to around 114-115 volts or so and the radios transformer just gets warm now. I think it was running at the edge of design tolerance. Tranformer would get hot after about 2 hours of usage at 124-125 volts. Now after two hours it's just warm.

[magicbrainman]

these models are terrible about the plastic dial cover shrinking, cracking, warping.

do not move south to hot climates, keep it away from any possibility of sun exposure, and keep your house climate controlled. If you have any spare plastic dials for this one or have had a repro made, please contact me magicbrainman on youtube. Also any part you need for this radio please inquire

[Lockemeister]

@smeezekitty I'm not saying you NEED to lower the input AC voltage. I had to because after a few hours the radio's transformer was getting boarderline hot. If your Plate voltage is too high, or the grid voltages is wrong, you have to check the circuit resistors first to see if they are in tolerance. If the tube is turned on too much it will run hot.

[Lockemeister]

@smeezekitty Check out my video on voltages. I ened up using an autotransformer to lower the voltage to this radio about 10 volts. I originally had 122-124 Volts input now I have 114-117 Volts AC input. I got the plate volatages to the 6F6 to about 365 Volts which is a nice voltage. Previously it was barely in spec at 395 Volts.

[Lockemeister]

@smeezekitty That's a good question. I do not know. I have never taken the temperture of the 6F6 output tubes. However, they are amoung the hottest running output tubes. I suggest getting the parameter table for the 6F6 tube, its the same as the 42 output tube and determine if your plate and grid voltages are within specs.