My schematic shows 310 VAC ( AC measurement ?) going to pin 6 and 1 of the 6X4. Where is that measured from? Then 210V out of pin 7 which is DC v to negative chassis right? The filter caps go to chassis. Thanks.

yes you should have AC on the plates of the rectifier and DC on the cathode

Sounds like a '53 Desoto radio. Off the top of my head you should see around 310 volts AC from each leg of the power transformer (going to 6X4 plates, pins 1 and 6) between each pin and the chassis. Pin 7 should be 220 or so volts DC between it and the chassis. If you power up the audio/power supply chassis without the radio connected, these voltages will be higher.

I generally avoid measuring the AC voltage across the power transformer secondary. IIRC the digital meter I use is limited to 750 volts AC. I do a lot of vibrator refurbishing and test them often in a test jig comprised of an old car radio power supply chassis with a power transformer, resistors and a buffer cap. Running a vibrator unloaded can result in some pretty high voltages on the transformer secondary, especially if your input voltage creeps up to 8 or 9 volts. I know I smoked one meter after accidentally measuring what was probably over 1000 VAC. My poor bench housekeeping (which I am battling but losing) once got me a very nasty shock. I had a 12 volt vibrator I was testing haywire test-lead conneted to my test jig. I had been powering a radio at around 13 volts and when I connected the power supply to my unloaded test jig, I bet it was supplying 16-17 volts. With all the wires going everyplace, guess what I grabbed? Felt like being hit with a sledgehammer.

If those voltages are not there would the fault be with the vibrator or the rectifier or the filters? Thanks

One can expect the capacitors to be passed their use by date. But even that it is a car radio we should not put the cart before the horse.

The caps, in particular the padder on the vibrator, were notorious for punching through. The spikes fron the vibrator being the issue. That cap (often around 0.5mfd) should have a voltage rating of 1KV or more. 6X5 is notorious for going short.

Remove it (test if you can) & see if it runs without it? If not the fault will be within the vibrator power supply part of the unit. You should be able to hear the vibrator, if it fires up. Do not toss it until you have checked the caps in the PSU, as they will / can short it & stop it.

It is inevitable and preferable, that every old paper and electrolytic cap in the set is replaced if they are still in there?
Work on the vibrator part first, it should run without the 6X5 ( circuit?) if you are intending making this a worker. Then work on the radio part, which should be fairly conventional. Leaving the 6X5 out reduces the risk of damage if there is a fault in the radio part. Do do the best you can, at checking resistors as you go.

I have not serviced a lot of car radio's but they are not the only things (like my tube tester) that have vibrator PSU's.

Marc

The typical paper buffer cap is .005 to .01 @ 1600V, They suffer the same leakage deterioration as the other paper caps in the radio. Try to stay within 20% of the marked value for the replacement and err on the high side if possible.
For a .008 Ive been using a .01/2000V disc marked "buffer" for a few decades now with no long term problems as reported by many customers and shops.

The 6X4 is a fairly reliable rectifier but I would not subject it to a no load test. Replace the electrolytics and a couple paper caps first before turning on and then finish the overhaul.

Carl

There may be a need for clarification. I am not suggesting running the rectifier with no load. I am suggesting leaving it out entirely, until such time as the PSU is sorted. With it on the bench it cannot supply B+ rendering the condition of the caps etc in the radio section, not associated with any filtering of the heaters, irrelavant at this point.

You will still get AC on the plate terminals of its socket, when the PSU is got going.

Marc

Thanks. A previous repairman jumped a new 30/450 across the canned 30/450 and did not disconnect the old.

Some who claimed to be repairmen did that sort of thing; Expedient, downright slack and absolutely not clever. On that basis, beware of other shortcuts & wrong parts that may have been substituted by this character. Any part that does not look like it belongs to the era of the radio, should be treated with suspicion & referred back to the schematic, if you have one?

Marc

Also previously installed are two capacitors: .022/200 from pin 7 of the 6AV6 to/from pin 7 of one 6AQ5. And .00118/1200 from a fat pin of vibrator where the 2 resistors go to chassis to pin 6 of 6X4. There is no DC on pin 7 of 6X4.

Be care full the cart is starting to get ahead of the horse. We need to apply the brakes. If there is no voltage on the plates of the 6X4, there is not in the creation of tomcats, going to be any on the cathode if the Vibrator PSU is not working.

You need to find a circuit or, trace out the Vibrator PSU first and identify it's parts. Most of them followed a similar plot. Untill you do that I don't think turning it on is going to acheive much.

6X4 Anodes are pins 1 & 6, Heaters 3 & 4 Which might have filtercaps on them? Pin 7 is the cathode. Pins 2 & 5 are not connected within the tube and could have anything on them (tags of convenience).

Pin 6 of 6AQ5 is it's screen and would likely go to B+ via a decoupling resistor of filter choke and would be connected to one of the filer caps & often a non polarised,decoupling cap. Pin 7 of 6AV6 is its plate. I would expect a resistor from pin 6 of 6AQ5 to pin 7 of 6AV6 and a cap from the 6AV6 to go to either pin 1 or 7 (grid 1) of the 6AQ5. These are not by the look of it vibrator circuit parts.

Is this a four or six pin Vibrator? Two of its pins are going to end up on the primary of the vibrator transformer. Without a schematic many of us are being forced to guesswork.

Marc

I have correct AC voltage on pins 1 and 6 of 6X4. Nothing out on pin 7. 4 pin vibrator.

Insuficient initial update data. If there is 310V on the plates of the 6X4 then the vibrator part is working. Loose interest in it. You now have to move to the PSU of the radio, viz 6X4. It is either a short on the output side of the 6X4 or it. See if it has open heaters, or no volts too them. You could breifly disconnect the cathode & breifly see if volts appear?

Marc

The AC to the 6X4 is about 250 not 310. The DCV on pin 7 are now just above 55-60 area (and to the FCS). (With the 6X4 out there is no DCV on pin 7.) Far less than the 210 on the schematic. I also disconnected the pin 7 lead to the FCS and there was no DC at all on pin 7. Re installed the lead and DC goes up to about 55. Pin 3 and 4 have about 4.5 DCV.
Thanks.

As suggested earlier.....REPLACE the electrolytics and paper caps before you destroy something such as the tube or transformer.

Carl

The heater voltage needs to be looked at. however there could be bad caps on that pulling it down assuming the source power is up to the task.

Low voltage B+, as has been suggested before, is likely due to exceesive load due to leaking capacitors etc. It is pointles trying fault find with old worn out paper caps & electrolytics, still in there. They are likely to be the fault.

Marc

I need the wattage on resistor R22 between the two filter caps. My schematic shows 2200 but no wattage. I also need R23 which is shown as 220K but no wattage. R22 is large and R23 is small. And can you send the two so that I do not need to pay minimum fee to Radio Daze. Thanks if you can.

Don't have the schematic to look at.

I believe this is the power section of the schematic Del is using:


Resistor R22 is a 2200Ω 2 watt. Sams shows the 6X4 plate voltage as 235vac as opposed to this schematic’s 310vac. I agree with the others that the low B+ voltage is probably due to a leaky or shorted section/sections of C25 electrolytic can------another clue is that he now needs another R22.

I replaced all three filter caps and no change. Also other caps in the Power Supply. Touched the 2200 (R22) resistor and it was HOT. Removed that lead and had 200DC to that point (schematic shows 210). Previously had 50DC. So I need R 22 (2200 at 2 watt) and R23 which is 220K but what wattage. 220K is 220,000? It looks like maybe 1 watt or even 1/2 watt looking at its size.