Transformer help

[mike60510]

I purchased and salvaged a power transformer from a Regency MR-10D Monitoradio. The transformer is a model 500-802 and has the EIA manufacturer code 831 (Triad). I cant find a spec sheet for the unit. The transformer from powered seven tubes and puts out 384 volts at the secondary side. I wanted to use it to build a Champ clone. Can anyone give me some guidance on how to determine if the transformer has adequate power for a Champ clone (12AX7, 6V6 or 6L6 and 5Y3)?

Thanks in advance

[nickb]

I purchased and salvaged a power transformer from a Regency MR-10D Monitoradio. The transformer is a model 500-802 and has the EIA manufacturer code 831 (Triad). I cant find a spec sheet for the unit. The transformer from powered seven tubes and puts out 384 volts at the secondary side. I wanted to use it to build a Champ clone. Can anyone give me some guidance on how to determine if the transformer has adequate power for a Champ clone (12AX7, 6V6 or 6L6 and 5Y3)?

Thanks in advance

It would be OK for single ended 6V6 or EL84 (6AQ5) type amp. I expect the HT secondary is center tapped to give 192-0-192 or about 250VDC after rectification.

Update: I looked at the schematic the MR-10D and I see it used a 6X4 for the rectifier and gave 190V DC out. You'll get a bit more on the HT if you use silicon rectifiers but it''s going to be rather low power output maybe a little over 2 watts.

[mike60510]

It would be OK for single ended 6V6 or EL84 (6AQ5) type amp. I expect the HT secondary is center tapped to give 192-0-192 or about 250VDC after rectification.

Update: I looked at the schematic the MR-10D and I see it used a 6X4 for the rectifier and gave 190V DC out. You'll get a bit more on the HT if you use silicon rectifiers but it''s going to be rather low power output maybe a little over 2 watts.

Thanks for the help. Yes, it is center taped and I did measure 192 volts like you mentioned. Would the 6X4 work better than the 5Y3?

[mike60510]

I starting to think that this transformer may not be a good candidate for what I'm hoping to accomplish.

[nickb]

Thanks for the help. Yes, it is center taped and I did measure 192 volts like you mentioned. Would the 6X4 work better than the 5Y3?

You are confusing AC measurements before the rectifier with the DC after.

When you measure the ACV on the transformer you are measuring the RMS value. RMS means that if that AC supply were connected a resistor it would dissipate the same amount of heat as a DC supply of the same voltage. When you pass an AC waveform through a rectifier and capacitor the output reaches the peak value of the AC input i.e. DCV = 1.41 x ACV ignoring the drop in the rectifier.


The original had 190VDC on the B+ under load ( i.e. when running). Therefore the ACV in = 190/1.4 = 134, if we allow for the voltage drop across the rectifier this is probably more like 155V. Now this is under load. When you are measuring the transformer you are doing so without a load so the voltage will be higher (say about 15%) now we are up to 178V getting close to the number you measure.

No, you can't use a 5Y3 as it has a 5V heater and this transformer only has 6.3V. That is one reason I suggest you use silicon rectifiers rather than a tube. Also (1) you get a higher b+ voltage =more power (2) The load on the transformer will be reduced = better life or more audio output (pick one) (3) They are much cheaper.

If a couple of watts is good for you then this transformer will be fine. Perhaps think of a small novelty build in reproduction vintage radio format cabinet- cool big dials and warm incandescent lamps.

[mike60510]

You are confusing AC measurements before the rectifier with the DC after.

When you measure the ACV on the transformer you are measuring the RMS value. RMS means that if that AC supply were connected a resistor it would dissipate the same amount of heat as a DC supply of the same voltage. When you pass an AC waveform through a rectifier and capacitor the output reaches the peak value of the AC input i.e. DCV = 1.41 x ACV ignoring the drop in the rectifier.


The original had 190VDC on the B+ under load ( i.e. when running). Therefore the ACV in = 190/1.4 = 134, if we allow for the voltage drop across the rectifier this is probably more like 155V. Now this is under load. When you are measuring the transformer you are doing so without a load so the voltage will be higher (say about 15%) now we are up to 178V getting close to the number you measure.

No, you can't use a 5Y3 as it has a 5V heater and this transformer only has 6.3V. That is one reason I suggest you use silicon rectifiers rather than a tube. Also (1) you get a higher b+ voltage =more power (2) The load on the transformer will be reduced = better life or more audio output (pick one) (3) They are much cheaper.

If a couple of watts is good for you then this transformer will be fine. Perhaps think of a small novelty build in reproduction vintage radio format cabinet- cool big dials and warm incandescent lamps.

Thanks for the assistance and technical information. Its truly appreciated.