Newb Stumped on a Derwent - Page 7 - UK Vintage Radio Repair and Restoration Discussion Forum

oldticktock · 21st Dec 2009, 12:17 am

6v between 4 & 5

the other end of the resistor went to pin 4 of the 42

Steve_P · 21st Dec 2009, 12:20 am

Question - is there a resistor between Pin 4 and Chassis right now. Yes or no?

Cheers,

Steve P.

oldticktock · 21st Dec 2009, 12:25 am

Quote:

Originally Posted by Steve_P

Question - is there a resistor between Pin 4 and Chassis right now. Yes or no?

Cheers,

Steve P.

yes

electrogram · 21st Dec 2009, 12:26 am

Quote:

Originally Posted by Station X

Steve P.

[The 75 is a triode and two diodes in the same envelope. They have a common cathode. Therefore the cathode current of all four valves (42 and 75) will flow through the cathode resistor. I'm wondering if it should be a lower value than 500ohms? It might be a body, tip spot type of 450 ohms. ] ]

Post 87 says 75 has its own bias resistor of 5000 ohms

Steve_P · 21st Dec 2009, 12:27 am

Does it measure OK? 500 Kohms or so?

Cheers,

Steve P.

oldticktock · 21st Dec 2009, 12:28 am

510k to be exact or 510,000

Steve_P · 21st Dec 2009, 12:30 am

Fine. Have you got a scope I wonder?

Cheers,

Steve P.

Station X · 21st Dec 2009, 12:32 am

Quote:

Originally Posted by electrogram

Post 87 says 75 has its own bias resistor of 5000 ohms

It actually says he measured 5000 ohms, which isn't the same thing. Also the drawings show the cathodes of the 42 and the 75 connected together. It doesn't look right to me, but that's how it is.

Station X · 21st Dec 2009, 12:35 am

Quote:

6v between 4 & 5

That's low, it should be the same as the cathode voltage ie 23V. Is THAT capacitor disconnected? If not measure again with THAT capacitor disconnected. Get rid of the surplus 510K resistor too.

oldticktock · 21st Dec 2009, 12:35 am

Quote:

Originally Posted by Steve_P

Fine. Have you got a scope I wonder?

Cheers,

Steve P.

I have a solatron ct160 but believe me that was bought with the intention of using when i'm grown up. also not been powered up for 3 years so will need to do so slowly on the variac

oldticktock · 21st Dec 2009, 12:39 am

hmm

Steve_P · 21st Dec 2009, 12:40 am

Pity. We could have looked for the Audio.

It's unlikely that THAT capacitor is faulty, but it happened to me once, so it's possible.

Cheers,

Steve P.

oldticktock · 21st Dec 2009, 12:45 am

Quote:

Originally Posted by Steve_P

Pity. We could have looked for the Audio.

It's unlikely that THAT capacitor is faulty, but it happened to me once, so it's possible.

Cheers,

Steve P.

your up for giving me pain arn't you .......

can you imagine numpty boy and an oscilloscope. I bought a book "Understanding oscilloscopes and display waveforms", these guys are mad!!!

Sean Williams · 21st Dec 2009, 12:47 am

Im really wondering if we could have a piccy of the whole underside of the chassis - this is just an overgrown US midget set, so really shouldn't present this much trouble getting the audio stage to work reliably!

I also think we need to standardise on some terminology here.....

Steve_P · 21st Dec 2009, 12:49 am

He's right, we should. But, looking at the picture that OTT drew, I would like to disconnect the tone control and try it.

Cheers,

Steve P.

oldticktock · 21st Dec 2009, 12:49 am

Quote:

Originally Posted by Sean Williams

Im really wondering if we could have a piccy of the whole underside of the chassis - this is just an overgrown US midget set, so really shouldn't present this much trouble getting the audio stage to work reliably!

I also think we need to standardise on some terminology here.....

Underside already posted not sure how far back probably page 4,5 or 6. On the main holding (domestic) you can see all the attachments i thin its "derchas"

oldticktock · 21st Dec 2009, 12:51 am

a photo was taken here it is again

Oops it won't let me load same one anyway its not correct now as the 50uf is back in place the right way round.

electrogram · 21st Dec 2009, 1:01 am

Quote:

Originally Posted by Station X

Quote:

Originally Posted by electrogram

Post 87 says 75 has its own bias resistor of 5000 ohms

It actually says he measured 5000 ohms, which isn't the same thing. Also the drawings show the cathodes of the 42 and the 75 connected together. It doesn't look right to me, but that's how it is.

Are you saying cathode current of 42 passes through both 470 and the 'measured' 5000, but in that case the 510k on pin 4 of 42 might better be returned to junction of the two resisrors the 540 and 5000, that is pin 5 cathode pin of 75, therefore the only error in post 53 is that 510k was connected to pin 5 not 4 of 42

oldticktock · 21st Dec 2009, 1:11 am

Quote:

Originally Posted by Station X

Quote:

6v between 4 & 5

That's low, it should be the same as the cathode voltage ie 23V. Is THAT capacitor disconnected? If not measure again with THAT capacitor disconnected. Get rid of the surplus 510K resistor too.

as requested and 23v is the result

Station X · 21st Dec 2009, 1:22 am

So with THAT capacitor connected you get 6V between pins 4 and 5 of the 42, and with that capacitor disconnected you get 23V between pins 4 and 5?

If that's the case then THAT capacitor is faulty.

21st Dec 2009, 12:17 am	#121
oldticktock Retired Dormant Member Join Date: Nov 2009 Location: Weardale, UK. Posts: 1,981	Re: Newb Stumped on a Derwent 6v between 4 & 5 the other end of the resistor went to pin 4 of the 42

21st Dec 2009, 12:20 am	#122
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Newb Stumped on a Derwent Question - is there a resistor between Pin 4 and Chassis right now. Yes or no? Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

21st Dec 2009, 12:27 am	#125
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Newb Stumped on a Derwent Does it measure OK? 500 Kohms or so? Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

21st Dec 2009, 12:28 am	#126
oldticktock Retired Dormant Member Join Date: Nov 2009 Location: Weardale, UK. Posts: 1,981	Re: Newb Stumped on a Derwent 510k to be exact or 510,000

21st Dec 2009, 12:30 am	#127
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Newb Stumped on a Derwent Fine. Have you got a scope I wonder? Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

21st Dec 2009, 12:39 am	#131
oldticktock Retired Dormant Member Join Date: Nov 2009 Location: Weardale, UK. Posts: 1,981	Re: Newb Stumped on a Derwent hmm

21st Dec 2009, 12:40 am	#132
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Newb Stumped on a Derwent Pity. We could have looked for the Audio. It's unlikely that THAT capacitor is faulty, but it happened to me once, so it's possible. Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

21st Dec 2009, 12:47 am	#134
Sean Williams Dekatron Join Date: Feb 2005 Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW Posts: 3,517	Re: Newb Stumped on a Derwent Im really wondering if we could have a piccy of the whole underside of the chassis - this is just an overgrown US midget set, so really shouldn't present this much trouble getting the audio stage to work reliably! I also think we need to standardise on some terminology here..... __________________ Engineers make things work and have spare bits when finished

21st Dec 2009, 12:49 am	#135
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Newb Stumped on a Derwent He's right, we should. But, looking at the picture that OTT drew, I would like to disconnect the tone control and try it. Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

21st Dec 2009, 12:51 am	#137
oldticktock Retired Dormant Member Join Date: Nov 2009 Location: Weardale, UK. Posts: 1,981	Re: Newb Stumped on a Derwent a photo was taken here it is again Oops it won't let me load same one anyway its not correct now as the 50uf is back in place the right way round. Last edited by oldticktock; 21st Dec 2009 at 12:57 am.

21st Dec 2009, 1:22 am	#140
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Newb Stumped on a Derwent So with THAT capacitor connected you get 6V between pins 4 and 5 of the 42, and with that capacitor disconnected you get 23V between pins 4 and 5? If that's the case then THAT capacitor is faulty. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.