Perdio PR73 current - UK Vintage Radio Repair and Restoration Discussion Forum

poppydog · 29th Jan 2019, 12:00 am

I have a Perdio Continental PR73 and have got it running off a PP9 with the other battery connector bridged as in this thread,

https://www.vintage-radio.net/forum/...ead.php?t=9068

When connected to my power supply it's drawing around 40ma no signal, does this sound about right? Or is it high?

Regards
Poppydog

Nuvistor · 29th Jan 2019, 12:08 am

Seems at least twice as high as it should be to me.

poppydog · 29th Jan 2019, 9:25 am

It does seem high thats why I posted, it sounds ok no distortion but cuts out if you touch the board. The board is only held on with 3 screws and one of them is missing so the board is a bit floppy, made worse by a pair of transformers at one end. I may well have a crack in it, it came to me via courier, need I say more

.
If anyone has one I would appreciate if they could have a look at theirs and see what current is being drawn.
Regards Poppydog

buggies · 29th Jan 2019, 7:16 pm

Have you checked the output stage current?

poppydog · 29th Jan 2019, 8:38 pm

Quote:

Originally Posted by buggies

Have you checked the output stage current?

I found a very hot oc81 so I took it out of circuit and the current has dropped to around 11.5ma

. I will look for replacements for the output pair (I've run out of oc81s) then do the usual checks.
regards poppydog

crackle · 29th Jan 2019, 8:58 pm

I would check the quiescent current as buggies suggested before replacing an OC81s.
Have you got the correct circuit for this, there are 2 versions, which one have you got?.
The later version has a trimmer pot to set the quiescent current in the output pair of OC81s
Have you checked and replaced any faulty electrolytics?

Mike

poppydog · 29th Jan 2019, 10:14 pm

The current will be checked, I will be looking to replace both the output transistors, the 1 that got hot was very hot and as stated I don't have any oc181s or AC128s left so will be replacing them with AC121s or AC153s. I have the later version, and am working from the sheet that is pasted to the back cover of the radio. I have replaced 1 cap so far which is c20 a 125uf 2.5v on the emitter of g4. I will however be checking them all at some point.

Regards Poppydog

Paul JD · 30th Jan 2019, 1:06 pm

Just did a quick check on mine and it is drawing 38 mA (switched to MW with no station tuned and volume control at min, ammeter connected in series with battery).

I have never done any work on mine so don't know if this is as it should be but it seems to be working perfectly and has always done so ever since my Father bought it in 1959.

GeoffK · 30th Jan 2019, 2:22 pm

The quiescent current of a similar Perdio Town and Country is around 12mA which is

more typical. 38mA is far too high, either the output transistors are getting warm,

possibly due to incorrect biasing or just getting leaky, or there is a very leaky capacitor

drawing the current. Apart from anything else it will drain the battery much quicker.

The Perdio PR73 is set up by adjusting VR2 to measure 135mV across R21 a 39 Ohm resistor in

the emitter of TR5, (this is with a 20KOhm/Volt meter), this sets 3mA bias in the driver

stage and correct bias to the output transistors.

poppydog · 30th Jan 2019, 6:13 pm

Quote:

Originally Posted by Paul JD

Just did a quick check on mine and it is drawing 38 mA (switched to MW with no station tuned and volume control at min, ammeter connected in series with battery).

I have never done any work on mine so don't know if this is as it should be but it seems to be working perfectly and has always done so ever since my Father bought it in 1959.

Thanks for bothering/taking the time to measure the current on your perdio PaulJD. I was beginning to wonder if I was the one and only member on here to own a pr73, however it looks like there are two of us

Regards Poppydog

Herald1360 · 30th Jan 2019, 10:26 pm

I'd be a bit wary about the bias setting instructions- they simply set the base bias voltage on the output devices. This can vary quite a bit for different transistor types, with dramatic effects on idle current.. Trouble is, there's no easy way to measure the output stage current directly since there's no emitter resistor(s) only the winding resistance in the output transformer.

Tweaking for an overall set current of around 12-15mA would probably be about right. That should give around 3-5mA in each half of the output.

The transistors should ideally be matched, too, for lowest distortion- not so easy without a bag of them to play with.

poppydog · 6th Feb 2019, 12:09 pm

Have managed to find a couple of matched AC153Y transistors and have just tacked them in, after some adjustment to the bias resistor the current is a bit more respectable now. Seems someone has been in here before me as the bias resistor had to be turned back a fair way. Also there is a lot of differences between schematics and whats actually on the board, which made things confusing.
poppydog

Herald1360 · 6th Feb 2019, 12:12 pm

If the current's respectable and the sound's acceptable, result!

poppydog · 8th Feb 2019, 8:50 pm

Some way out of spec resistors have been changed as have all the elec caps The tcc caps were especially bad, worse than the red and yellow plesseys that were in there. Not really a fan of the look of the modern replacement components on the board but they are all good quality.
Voltages are now very good as is the current now being drawn, around 11ma no signal, which is better than the 40ma previously.
I have a bright missing off one of the knobs and the perdio badge is missing so I will put a request in the sets wanted section
Very good sensitivity and the sound is now excellent, yes it is “a result”

Some pics below.

Regards
Poppydog

29th Jan 2019, 12:00 am	#1
poppydog Banned Join Date: Oct 2015 Location: Cornwall, UK. Posts: 849	Perdio PR73 current I have a Perdio Continental PR73 and have got it running off a PP9 with the other battery connector bridged as in this thread, https://www.vintage-radio.net/forum/...ead.php?t=9068 When connected to my power supply it's drawing around 40ma no signal, does this sound about right? Or is it high? Regards Poppydog

29th Jan 2019, 12:08 am	#2
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	Re: Perdio PR73 current Seems at least twice as high as it should be to me. __________________ Frank

29th Jan 2019, 9:25 am	#3
poppydog Banned Join Date: Oct 2015 Location: Cornwall, UK. Posts: 849	Re: Perdio PR73 current It does seem high thats why I posted, it sounds ok no distortion but cuts out if you touch the board. The board is only held on with 3 screws and one of them is missing so the board is a bit floppy, made worse by a pair of transformers at one end. I may well have a crack in it, it came to me via courier, need I say more. If anyone has one I would appreciate if they could have a look at theirs and see what current is being drawn. Regards Poppydog

29th Jan 2019, 7:16 pm	#4
buggies Heptode Join Date: Jan 2009 Location: West Lothian, UK. Posts: 762	Re: Perdio PR73 current Have you checked the output stage current? Attached Thumbnails __________________ George

29th Jan 2019, 8:58 pm	#6
crackle Rest in Peace Join Date: Mar 2011 Location: Basildon, Essex, UK. Posts: 4,100	Re: Perdio PR73 current I would check the quiescent current as buggies suggested before replacing an OC81s. Have you got the correct circuit for this, there are 2 versions, which one have you got?. The later version has a trimmer pot to set the quiescent current in the output pair of OC81s Have you checked and replaced any faulty electrolytics? Mike Last edited by crackle; 29th Jan 2019 at 9:05 pm.

29th Jan 2019, 10:14 pm	#7
poppydog Banned Join Date: Oct 2015 Location: Cornwall, UK. Posts: 849	Re: Perdio PR73 current The current will be checked, I will be looking to replace both the output transistors, the 1 that got hot was very hot and as stated I don't have any oc181s or AC128s left so will be replacing them with AC121s or AC153s. I have the later version, and am working from the sheet that is pasted to the back cover of the radio. I have replaced 1 cap so far which is c20 a 125uf 2.5v on the emitter of g4. I will however be checking them all at some point. Regards Poppydog

30th Jan 2019, 1:06 pm	#8
Paul JD Pentode Join Date: Oct 2018 Location: Coventry, West Midlands, UK. Posts: 220	Re: Perdio PR73 current Just did a quick check on mine and it is drawing 38 mA (switched to MW with no station tuned and volume control at min, ammeter connected in series with battery). I have never done any work on mine so don't know if this is as it should be but it seems to be working perfectly and has always done so ever since my Father bought it in 1959.

30th Jan 2019, 2:22 pm	#9
GeoffK Heptode Join Date: Mar 2016 Location: Essex, UK. Posts: 602	Re: Perdio PR73 current The quiescent current of a similar Perdio Town and Country is around 12mA which is more typical. 38mA is far too high, either the output transistors are getting warm, possibly due to incorrect biasing or just getting leaky, or there is a very leaky capacitor drawing the current. Apart from anything else it will drain the battery much quicker. The Perdio PR73 is set up by adjusting VR2 to measure 135mV across R21 a 39 Ohm resistor in the emitter of TR5, (this is with a 20KOhm/Volt meter), this sets 3mA bias in the driver stage and correct bias to the output transistors. __________________ *Geoff*

30th Jan 2019, 10:26 pm	#11
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: Perdio PR73 current I'd be a bit wary about the bias setting instructions- they simply set the base bias voltage on the output devices. This can vary quite a bit for different transistor types, with dramatic effects on idle current.. Trouble is, there's no easy way to measure the output stage current directly since there's no emitter resistor(s) only the winding resistance in the output transformer. Tweaking for an overall set current of around 12-15mA would probably be about right. That should give around 3-5mA in each half of the output. The transistors should ideally be matched, too, for lowest distortion- not so easy without a bag of them to play with. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

6th Feb 2019, 12:09 pm	#12
poppydog Banned Join Date: Oct 2015 Location: Cornwall, UK. Posts: 849	Re: Perdio PR73 current Have managed to find a couple of matched AC153Y transistors and have just tacked them in, after some adjustment to the bias resistor the current is a bit more respectable now. Seems someone has been in here before me as the bias resistor had to be turned back a fair way. Also there is a lot of differences between schematics and whats actually on the board, which made things confusing. poppydog

6th Feb 2019, 12:12 pm	#13
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: Perdio PR73 current If the current's respectable and the sound's acceptable, result! __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

8th Feb 2019, 8:50 pm	#14
poppydog Banned Join Date: Oct 2015 Location: Cornwall, UK. Posts: 849	Re: Perdio PR73 current Some way out of spec resistors have been changed as have all the elec caps The tcc caps were especially bad, worse than the red and yellow plesseys that were in there. Not really a fan of the look of the modern replacement components on the board but they are all good quality. Voltages are now very good as is the current now being drawn, around 11ma no signal, which is better than the 40ma previously. I have a bright missing off one of the knobs and the perdio badge is missing so I will put a request in the sets wanted section Very good sensitivity and the sound is now excellent, yes it is “a result” Some pics below. Regards Poppydog Attached Thumbnails