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 Post subject: EMUD 713 Power Supply
PostPosted: Dec Mon 05, 2022 10:05 pm 
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Joined: Nov Sun 27, 2011 7:06 pm
Posts: 47
Location: Rockwall, TX
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Well progress is measured one connection at a time. I have the radio AM/FM/SW working. I replaced the output tube and recapped all paper and electrolytics.

My concern is the high voltage in the circuit. For some reason the prints indicate 225V at the EL84 pin 7.. I am getting $278.. I backtracked most of the resistors and readings from EZ80. My AC on the transformer is 280AC but pin 3EZ80 = 310V .. My 2 ecaps replace with 47UF 350 measure 85 UF in circuit. Should this be higher? Would low Uf cause this issue? Could it be the EZ80? *Note I am testing without the ancillary preamp EC83or phono plugged into the radio.

Am I chasing this in the wrong area. Any suggestion to help bring down that voltage to normal ?


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 Post subject: Re: EMUD 713 Power Supply
PostPosted: Dec Tue 06, 2022 6:40 am 
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Joined: Apr Fri 28, 2006 11:46 am
Posts: 1199
Hello Radioguy52!
If you take 50 µF or 47µF, it doesn´t matter, electrolytic caps have a wide tolerance.
A 47µF of today is a 50µF of yesterday.
You have no EC 83 (ECC 83) but a EABC 80!
If I understand you right, the radio works perfect?
A too high voltage indcates me that one of the stages doesn´t take it`s right power.
(The power supply is not regulated.)
As far you have the original power transformer!

Is it right, you own a US-version with only 117V/AC mains?
Are all plate voltages too high?

It could be possible, that there is an error in the schematic.
Check at the tube data for the right (plate) voltages to operate the EL 84 and the other tubes.

Older radios had often a coil to reduce the hum.
If there is no one or a wrong one, you can try to add one between the two 47µF caps.
(There has to be a resistor, what´s it´s right value?)

Please don´t forget to check the cathode- and grid-resistor of the EL 84!

Regards,
SIXMILLION DOLLARMAN

_________________
From all the things I ever lost I miss my mind the most
ScottyBeamMeUpThereIsNo 4/3-TV/AM OnEarth


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 Post subject: Re: EMUD 713 Power Supply
PostPosted: Dec Tue 06, 2022 4:11 pm 
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Joined: Nov Sun 27, 2011 7:06 pm
Posts: 47
Location: Rockwall, TX
Yes US unit. Apears to be original Xformer. I have taken reading on the original photo and here are more for the EL4 slot (6BQ5 )

1) The original EL84 tested very weak. I ordered a NOS 6BQ5 (Test strong on my Hickock)
2) EL84 Test Points as follows
Pin 1 Not used
Pin 2 .0004 Varies +- with volume
Pin 3 8.3V
Pin 4, 5 0V Pin
Pin 6 NC
Pin 7 281V ---- Note Pin 7 has a 2000pf to ground ca not shown in the schematic? Maybe for noise suppression?
Pin 8
Pin 9 285V

570 ohms across Pin 7 and EZ80 3
15 Ohms xformer to top of good 1000 R45

Original Work : Replaced Caps, Replace Open R39. (That was the original issue, Replaced R40 with a 33K. It was wrong in the unit. (had a 2oK ohm) All others apear match the schematic.
I reviewed the resistors in circuit. Especially around the 6BQ5. (Plate is rated 300V)


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 Post subject: Re: EMUD 713 Power Supply
PostPosted: Dec Thu 08, 2022 3:07 pm 
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Joined: Nov Sun 27, 2011 7:06 pm
Posts: 47
Location: Rockwall, TX
My voltages are ALL running higher than the schematic calls for. 225V vs 280V on the output stage for instance. I have been up and down the entire output stage area under AM or Phono to see if any resistor is out of tolerance. As noted in my prior measurements. Nothing so far. Should I give up and run hotter or will I be sorry and cause more damage?


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 Post subject: Re: EMUD 713 Power Supply
PostPosted: Dec Thu 08, 2022 3:47 pm 
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Joined: Jan Mon 16, 2012 3:15 pm
Posts: 9673
Location: Brandon, Iowa USA
If I missed this in the thread up to this point, I apologize: but what is the AC voltage measured at the convenience outlet into which the radio is plugged?


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 Post subject: Re: EMUD 713 Power Supply
PostPosted: Dec Thu 08, 2022 7:01 pm 
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Joined: Nov Sun 27, 2011 7:06 pm
Posts: 47
Location: Rockwall, TX
Its on my variable at 117 V..AC


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