More PCR Questions - UK Vintage Radio Repair and Restoration Discussion Forum

RobinBirch · 13th Dec 2007, 7:57 pm

Hi Everyone,
Well, I've started putting the PCR back together but have a problem. The EMER that I have is a little confusing and very light on circuit values.

What component values there are are numbered as for the PCR 2 but the PCR/PCR1 circuit is numbered differently. Also in putting it all back as a PCR (as it was built) means that I have to find the value of 2 resistors that have been removed from the set.

In PCR numbring (if you have the EMER to hand) they are R4 and R16. R16 is in the grid lead for the VT52 and R4 goes from that to earth. The non earth end of R4 has the signal fed from the earlier stage through a coupling capacitor.

In the 6V6 circuit of the PCR2 there are two equivalent resistors that, according to the circuit sheet have values of 2.2k for the grid lead resistor and 10k for R4.

Given that the valves are different in the two circuits (EL32 vs a 6V6G) are these values reasonable for the EL32 circuit.

Robin

GMB · 13th Dec 2007, 8:58 pm

OK, I've finally got mine open.

It doesn't seem to be like the Emer circuit at all.
The O/P valve grid is grounded by a 470K resistor, and the coupling capacitor is just joined to the grid directly.

I have to admit that there is some modification in this area but the grid resistor looks original and unmodified.

The coupling capacitor disappears under the screened box so I can't see what else is going on without gutting it some more.

GMB · 13th Dec 2007, 9:18 pm

... and it looks like G1 is also joined to G3

That seems extraordinary but it looks original. The G1 connection (from top cap) comes through the chassis right by pin 5 (G3) and goes to it. The 470k resistor goes from there to ground.

MichaelR · 13th Dec 2007, 10:18 pm

According to my data , R4 is 10K and R16 is 500k. for the PCR

R16 via screened cable is connecting grid of output valve to junction of R4 and C21 as you would expect. C21 is anode coupling from previous stage, R4 connected to this and then down to earth.

In the PCR2 diagram the R4 resistor designation ( 10K) is equivalent to the R16 designation in the PCR circuit. The R11 designation (2.2K) in the PCR2 circuit is equivalent to the R16 designation in the PCR circuit.

Station X · 13th Dec 2007, 10:23 pm

My diagram for a PCR (PCR1) shows the coupling capacitor (C21) 0.005µF connected to earth via R4 (470K). the junction of C21 and R4 is connected to G1 of the VT52/EL32 via R16 (22K). The leads of R16 are screened.

No connection shown from G1 to G3. G3 is connected directly to earth.

GMB · 13th Dec 2007, 11:58 pm

Sorry - I missed it - there is a 22k grid stopper mounted well hidden on the actual top-cap connector.

So G1 goes via 22k to G3, which is joined to the coupling capacitor and 470k to ground. This is the actuality, not a diagram.

Station X · 14th Dec 2007, 1:17 pm

Strange that. Just about every suppressor grid I've ever seen has been taken either to the cathode or to earth. Still if that's how it's wired and it works......

Here's an extract from the circuit.

RobinBirch · 14th Dec 2007, 2:52 pm

Guys,
Thank you very much for this. I can go and get some resistors and wire this up.

StationX, MichaelR I guess from this you have some far better circuit diagrams and/or component lists than I do. Is there any chance of a scan?

Kind regards

Robin

Station X · 14th Dec 2007, 2:57 pm

I scanned my PCR stuff a while back. Drop me a PM with your email address and it's yours.

RobinBirch · 14th Dec 2007, 4:23 pm

PM on its way.

Many thanks

Robin

13th Dec 2007, 7:57 pm	#1
RobinBirch Hexode Join Date: Apr 2003 Location: Cotswolds, UK. Posts: 465	More PCR Questions Hi Everyone, Well, I've started putting the PCR back together but have a problem. The EMER that I have is a little confusing and very light on circuit values. What component values there are are numbered as for the PCR 2 but the PCR/PCR1 circuit is numbered differently. Also in putting it all back as a PCR (as it was built) means that I have to find the value of 2 resistors that have been removed from the set. In PCR numbring (if you have the EMER to hand) they are R4 and R16. R16 is in the grid lead for the VT52 and R4 goes from that to earth. The non earth end of R4 has the signal fed from the earlier stage through a coupling capacitor. In the 6V6 circuit of the PCR2 there are two equivalent resistors that, according to the circuit sheet have values of 2.2k for the grid lead resistor and 10k for R4. Given that the valves are different in the two circuits (EL32 vs a 6V6G) are these values reasonable for the EL32 circuit. Robin

13th Dec 2007, 8:58 pm	#2
GMB Dekatron Join Date: Aug 2003 Location: near Reading (and sometimes Torquay) Posts: 3,099	Re: More PCR Questions OK, I've finally got mine open. It doesn't seem to be like the Emer circuit at all. The O/P valve grid is grounded by a 470K resistor, and the coupling capacitor is just joined to the grid directly. I have to admit that there is some modification in this area but the grid resistor looks original and unmodified. The coupling capacitor disappears under the screened box so I can't see what else is going on without gutting it some more.

13th Dec 2007, 9:18 pm	#3
GMB Dekatron Join Date: Aug 2003 Location: near Reading (and sometimes Torquay) Posts: 3,099	Re: More PCR Questions ... and it looks like G1 is also joined to G3 That seems extraordinary but it looks original. The G1 connection (from top cap) comes through the chassis right by pin 5 (G3) and goes to it. The 470k resistor goes from there to ground.

13th Dec 2007, 10:18 pm	#4
MichaelR Retired Dormant Member Join Date: Mar 2006 Location: Sheffield, South Yorkshire, UK. Posts: 1,587	Re: More PCR Questions According to my data , R4 is 10K and R16 is 500k. for the PCR R16 via screened cable is connecting grid of output valve to junction of R4 and C21 as you would expect. C21 is anode coupling from previous stage, R4 connected to this and then down to earth. In the PCR2 diagram the R4 resistor designation ( 10K) is equivalent to the R16 designation in the PCR circuit. The R11 designation (2.2K) in the PCR2 circuit is equivalent to the R16 designation in the PCR circuit. Last edited by MichaelR; 13th Dec 2007 at 10:26 pm. Reason: ADDING FURTHER INFORMATION

13th Dec 2007, 10:23 pm	#5
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: More PCR Questions My diagram for a PCR (PCR1) shows the coupling capacitor (C21) 0.005µF connected to earth via R4 (470K). the junction of C21 and R4 is connected to G1 of the VT52/EL32 via R16 (22K). The leads of R16 are screened. No connection shown from G1 to G3. G3 is connected directly to earth. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

13th Dec 2007, 11:58 pm	#6
GMB Dekatron Join Date: Aug 2003 Location: near Reading (and sometimes Torquay) Posts: 3,099	Re: More PCR Questions Sorry - I missed it - there is a 22k grid stopper mounted well hidden on the actual top-cap connector. So G1 goes via 22k to G3, which is joined to the coupling capacitor and 470k to ground. This is the actuality, not a diagram.

14th Dec 2007, 1:17 pm	#7
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: More PCR Questions Strange that. Just about every suppressor grid I've ever seen has been taken either to the cathode or to earth. Still if that's how it's wired and it works...... Here's an extract from the circuit. Attached Thumbnails __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

14th Dec 2007, 2:52 pm	#8
RobinBirch Hexode Join Date: Apr 2003 Location: Cotswolds, UK. Posts: 465	Re: More PCR Questions Guys, Thank you very much for this. I can go and get some resistors and wire this up. StationX, MichaelR I guess from this you have some far better circuit diagrams and/or component lists than I do. Is there any chance of a scan? Kind regards Robin

14th Dec 2007, 2:57 pm	#9
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: More PCR Questions I scanned my PCR stuff a while back. Drop me a PM with your email address and it's yours. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

14th Dec 2007, 4:23 pm	#10
RobinBirch Hexode Join Date: Apr 2003 Location: Cotswolds, UK. Posts: 465	Re: More PCR Questions PM on its way. Many thanks Robin