Hi Chris,
Nothing wrong with an HP 331A ~ 339A. Lovely pieces of gear.
The biggest thing with tubes and Counterpoint is that the performance depends entirely on the tube. Including gain. Just try to find some well matched sections in the same tube. A dual tube is just a pair of individuals in the same glass. Hopefully close.
-Chris
Nothing wrong with an HP 331A ~ 339A. Lovely pieces of gear.
The biggest thing with tubes and Counterpoint is that the performance depends entirely on the tube. Including gain. Just try to find some well matched sections in the same tube. A dual tube is just a pair of individuals in the same glass. Hopefully close.
-Chris
Chris (Pars) - You mentioned that you'd got the service manual. Do you think it's worth getting this from Michael Elliott (especially when he says that some of the early ones were short)? I'm loath to spend US$75 for a manual if it's not worth it ...
Thanks
Stephen
Thanks
Stephen
Hi Stephen,
Don't feel bad. The early manuals weren't much, but they are more clear than the new "books" they made. I think that $75 USD is seriously steep for any Counterpoint product. I've seen manuals for real test gear go for less, and more. The difference was that those manuals were very clear. Some of the large Tascam manuals were less, and much better.
-Chris
Don't feel bad. The early manuals weren't much, but they are more clear than the new "books" they made. I think that $75 USD is seriously steep for any Counterpoint product. I've seen manuals for real test gear go for less, and more. The difference was that those manuals were very clear. Some of the large Tascam manuals were less, and much better.
-Chris
Hi Chris,anatech said:
I went ahead and got a pair of the 6922EH (got the gold pins, and they aren't the nice shiny smooth gold as you would see on Amperexs, etc., so probably not worth it). Lowered the noise floor significantly (it wasn't too bad before, not its pretty good). Haven't taken the time to listen to it yet, but I'm sure it will be fine.
One question for you: in the HV regulation section, there is one film cap (Wonder cap) among the electrolytics (think it is something like C56) that is only used for filtering (shown as an 8uf 200V cap) that is placed in the circuit from a ~260Vdc to ground point. What is the failure mode of most typical film caps? This would seem to be significantly over-voltage... would leakage here cause some noise (I know, pull it and find out
)?Thanks again,
Chris (Pars)
Hi - after a long delay, I finally managed to get round to some basic mods (changing the phono sockets and main volume pot). However, I've managed to mess something up, but can't figure out what. Before I go out and find a repair shop (not easy in Hong Kong ...), I wondered if anyone had any ideas. (NB: the tubes are all fine!)
The problem is this:
- all line inputs work OK.
- Channel B of the phono input doesn't work at all in stereo mode. In mono, I can get sound on both channels, but only if the Channel B balance pot is slightly attenuated. If it is left in its unattenuated position, the sound is completely muted on both channels. (This doesn't happen for the line inputs.)
- I've checked all voltages, and they're all broadly within spec apart from one. The voltage on the plate/anode of the second stage of the Channel B phono section should be 45-145v, but is only 4.5v. The B+ voltage on the other side of the anode resistor (a 27k 2w) is in spec at 250v.
- I've traced the Channel B phono section looking for bad solder joints, solder bridges, stray wires, etc. but I can't find anything.
Any ideas please?
Thanks
Stephen
The problem is this:
- all line inputs work OK.
- Channel B of the phono input doesn't work at all in stereo mode. In mono, I can get sound on both channels, but only if the Channel B balance pot is slightly attenuated. If it is left in its unattenuated position, the sound is completely muted on both channels. (This doesn't happen for the line inputs.)
- I've checked all voltages, and they're all broadly within spec apart from one. The voltage on the plate/anode of the second stage of the Channel B phono section should be 45-145v, but is only 4.5v. The B+ voltage on the other side of the anode resistor (a 27k 2w) is in spec at 250v.
- I've traced the Channel B phono section looking for bad solder joints, solder bridges, stray wires, etc. but I can't find anything.
Any ideas please?
Thanks
Stephen
IIRC, on these units, the phono section is cap coupled going in and out. Then the balance and volume are connected in a passive type arrangement as well as the mono switch. Thencomes the capactively coupled input to the line buffer and then capacitor out. It would seem to suggest that the problem lies directly in the one channel's phono section. All we know, is that it leaves lots of points where a better cap can be introduced to bring about better sound quality. (two in/out sets of capacitors, per channel!) each signal on a LP, goes through 4 coupling caps!
KBK - Thanks. You are right: there are four caps in the LP signal path. I'd contemplated removing the output coupling cap on the phono section (as this seems to me to be needed only for the tape output). However, I can't do this until I've figured out what my problem is.
(NB: The caps are all OK although the values do seem to be off spec. Not surprising given that they're 20yrs+ old.)
(NB: The caps are all OK although the values do seem to be off spec. Not surprising given that they're 20yrs+ old.)
Hi All,
No thread notification. Darn.
Hi Chris,
The failure mode for most film caps is open circuit. The arc self heals with the effect of reducing the capacitance slightly. Stick one in that is properly rated. As far as the tube is concerned, I expect it will sound better too. Tell me what you think. The lower noise and relative lack of microphonics is a welcome change. I found the distortion was lower as well.
Hi Stephen,
I disagree with removing any coupling caps in these. That's a disaster waiting to happen.
Your plate at 4.5 VDC. Measure the plate voltages with the tube removed. Also measure the voltage at the grid terminal. It is possible there is a piece of wire under the tube socket shorting grid to plate, or something similar.
Hi KBK,
Well, with those designs, all part changes are clearly audible. I have no doubt better caps may sound better.
-Chris
No thread notification. Darn.
Hi Chris,
The failure mode for most film caps is open circuit. The arc self heals with the effect of reducing the capacitance slightly. Stick one in that is properly rated. As far as the tube is concerned, I expect it will sound better too. Tell me what you think. The lower noise and relative lack of microphonics is a welcome change. I found the distortion was lower as well.
Hi Stephen,
I disagree with removing any coupling caps in these. That's a disaster waiting to happen.
Your plate at 4.5 VDC. Measure the plate voltages with the tube removed. Also measure the voltage at the grid terminal. It is possible there is a piece of wire under the tube socket shorting grid to plate, or something similar.
Hi KBK,
Well, with those designs, all part changes are clearly audible. I have no doubt better caps may sound better.
-Chris
Chris (Anatech)
Thanks. I'll leave the caps alone!
There's no wire, etc. beneath the tube sockets shorting anything out. I didn't measure voltages with the tubes out though, as I thought this would cause problems for the other tubes through the heater supply not being properly loaded by all four tubes (but maybe not a problem for the 5 minutes I'll need?). I'll measure the voltages with the tube removed and see what I get.
Thanks
Stephen
Thanks. I'll leave the caps alone!
There's no wire, etc. beneath the tube sockets shorting anything out. I didn't measure voltages with the tubes out though, as I thought this would cause problems for the other tubes through the heater supply not being properly loaded by all four tubes (but maybe not a problem for the 5 minutes I'll need?). I'll measure the voltages with the tube removed and see what I get.
Thanks
Stephen
Hi Stephen,
Just yank the problem tube and make your measurements. Can you take a picture and email me with it?
bhomester at gmail dot com
-Chris
Just yank the problem tube and make your measurements. Can you take a picture and email me with it?
bhomester at gmail dot com
-Chris
Chris - Many thanks. I've just made the measurements:
Plate/anode voltage - 4.07v (tube out); 3.93v (tube in)
Grid voltage - -0.51v (tube out); -0.61v (tube in)
I'll send some photos separately.
Thanks again
Stephen
Plate/anode voltage - 4.07v (tube out); 3.93v (tube in)
Grid voltage - -0.51v (tube out); -0.61v (tube in)
I'll send some photos separately.
Thanks again
Stephen
Hi Stephen,
Okay, that's what I expected. Turn off and discharge the supplies. Measure the plate to ground resistance. If it's very high, take the next steps.
Put the tube back in. Measure the voltage on both sides of the 27K plate resistor. It's specified at 2W. I use 3W units to replace these. It's possible the resistor is open. If the coupling cap was shorted, your plate voltage would be lower, but not 4~5 V.
There is a possibility that R59, a 499 R 1/4W resistor is open, but that would kill both phono output stages.
-Chris
Okay, that's what I expected. Turn off and discharge the supplies. Measure the plate to ground resistance. If it's very high, take the next steps.
Put the tube back in. Measure the voltage on both sides of the 27K plate resistor. It's specified at 2W. I use 3W units to replace these. It's possible the resistor is open. If the coupling cap was shorted, your plate voltage would be lower, but not 4~5 V.
There is a possibility that R59, a 499 R 1/4W resistor is open, but that would kill both phono output stages.
-Chris
Hi Stephen,
I'll bet one of the solder fillets are cracked between the main PCB and the tube PCB. Just resolder the lot. If you use liquid solder flux (for electronics!!) it will go much easier. Always support this board when changing tubes.
-Chris
I'll bet one of the solder fillets are cracked between the main PCB and the tube PCB. Just resolder the lot. If you use liquid solder flux (for electronics!!) it will go much easier. Always support this board when changing tubes.
-Chris
Chris - Many thanks.
I should have explained this before: I'd also measured the voltages directly at either side of the 27k resistor - 250v on the B+ rail to the PSU, and 4v on the side between the resistor and the plate. However, when I'd first measured the plate to ground resistance (with power off and on), the resistance value only slowly climbed to about 18k on Channel B. I had thought that this must be the problem, as the resistance climbed much more quickly on Channel A to 25k. So, I replaced the 27k resistors in both Channel A and B, but it had no effect at all - except that at least Channel A came up to nearly 27k. However, the resistance value on Channel B still climbs only slowly and never reaches 27k. I must have a short to ground somewhere - if only I could find it ...
I also suspected a bad joint between the boards and resoldered the connection between the two but only on the connection between the 27k resistor and the plate. Again, no change. Maybe I should try resoldering the other joints too.
What's frustrating is that I didn't mess around with any of this when I changed the RCA sockets and the volume pot. Oh well, I guess I'm learning - not sure what though!
Thanks again for your help.
Stephen
I should have explained this before: I'd also measured the voltages directly at either side of the 27k resistor - 250v on the B+ rail to the PSU, and 4v on the side between the resistor and the plate. However, when I'd first measured the plate to ground resistance (with power off and on), the resistance value only slowly climbed to about 18k on Channel B. I had thought that this must be the problem, as the resistance climbed much more quickly on Channel A to 25k. So, I replaced the 27k resistors in both Channel A and B, but it had no effect at all - except that at least Channel A came up to nearly 27k. However, the resistance value on Channel B still climbs only slowly and never reaches 27k. I must have a short to ground somewhere - if only I could find it ...
I also suspected a bad joint between the boards and resoldered the connection between the two but only on the connection between the 27k resistor and the plate. Again, no change. Maybe I should try resoldering the other joints too.
What's frustrating is that I didn't mess around with any of this when I changed the RCA sockets and the volume pot. Oh well, I guess I'm learning - not sure what though!
Thanks again for your help.
Stephen
Hi Stephen,
Well, you know, it could be the socket itself. Desolder it and power up again.
-Chris
Well, you know, it could be the socket itself. Desolder it and power up again.
-Chris
Chris - Thanks.
I was just thinking about whether the caps might be the problem. Their values do seem to me to be way off. The coupling cap between the phono section (on both channels) is specified as 0.047mF, but in my pre is actually an 8mF cap bypassed by a smaller capacitor. I'm currently at work and can't remember what they measured (and I know the measurement in circuit wouldn't give a wholly correct value), but I think the Channel B coupling cap was something like 1.4mF. I don't think I measured the value in Channel A.
Could this be it? (NB: the resistor between the plate and the coupling cap measures at 680, on spec.)
Stephen
I was just thinking about whether the caps might be the problem. Their values do seem to me to be way off. The coupling cap between the phono section (on both channels) is specified as 0.047mF, but in my pre is actually an 8mF cap bypassed by a smaller capacitor. I'm currently at work and can't remember what they measured (and I know the measurement in circuit wouldn't give a wholly correct value), but I think the Channel B coupling cap was something like 1.4mF. I don't think I measured the value in Channel A.
Could this be it? (NB: the resistor between the plate and the coupling cap measures at 680, on spec.)
Stephen
Hi Stephen,
A shorted coupling cap still would not take the B+ down to 4.5 VDC. It will see a 1 M ohm resistor and about 65 K ohm roughly if RIAA is selected, balance centered. I suspect something going on in the socket or the PCB under it. You might be able to see a carbon track glowing in darkness with the tube out. Maybe not. That's why I suggested that you remove the socket and test it. Also have a good look under the socket.
When you resoldered the connections between boards, did you remove all the flux? If not, do it and have a close look for shorts. Retest.
-Chris
Edit: Put the original capacitor values back in once you have it working. Polyprop. would be good.
A shorted coupling cap still would not take the B+ down to 4.5 VDC. It will see a 1 M ohm resistor and about 65 K ohm roughly if RIAA is selected, balance centered. I suspect something going on in the socket or the PCB under it. You might be able to see a carbon track glowing in darkness with the tube out. Maybe not. That's why I suggested that you remove the socket and test it. Also have a good look under the socket.
When you resoldered the connections between boards, did you remove all the flux? If not, do it and have a close look for shorts. Retest.
-Chris
Edit: Put the original capacitor values back in once you have it working. Polyprop. would be good.
phono in and out on a 5 and 5.1 pre, is a 0.47uf 250VDC cap. line in and out, is a 8.0uf 250VDC cap (or 200VDC rated for all, I can't quite recall). All 8 caps rae made by either Electrocube or Rel-Cap, and are PP film types. (NOT film & foil)
I've upgraded mine to Multi-caps,and bypassed with caps from my tiny horde of Polystyrene caps.
Hey Chris, How's it going? I've been off the board for a while, and I'm trying to bite my tounge in someone else's thread on plasma tweeters, when I mentioned that the second 'suggestion' of thermodynamics (he really DID call it a 'suggestion' when he proposed it!) was really and really IS that - a suggestion. For the same basic reasons a sane scientific investigator does such things. To use it as a theory, until something better comes along, like all theories involving science. Like the truth that there really are no facts -most folks can't live with that basic point of truth.
Then people get emotional, like they are a cat or somthing, and I'm holding them over a open toilet..and flushing. And their little legs get going, spinning away madly. Gosh. Some people need to get those world fearing emotions under control.
There. Now that I've vented some sort of response to their obviously emotional vitrol, I'll be ok.
yes yes.
I've upgraded mine to Multi-caps,and bypassed with caps from my tiny horde of Polystyrene caps.
Hey Chris, How's it going? I've been off the board for a while, and I'm trying to bite my tounge in someone else's thread on plasma tweeters, when I mentioned that the second 'suggestion' of thermodynamics (he really DID call it a 'suggestion' when he proposed it!) was really and really IS that - a suggestion. For the same basic reasons a sane scientific investigator does such things. To use it as a theory, until something better comes along, like all theories involving science. Like the truth that there really are no facts -most folks can't live with that basic point of truth.
Then people get emotional, like they are a cat or somthing, and I'm holding them over a open toilet..and flushing. And their little legs get going, spinning away madly. Gosh. Some people need to get those world fearing emotions under control.
There. Now that I've vented some sort of response to their obviously emotional vitrol, I'll be ok.
yes yes.
Hi Ken,
One schematic (SA-5) shows the RIAA coupling cap at 8 uF, the other (5.1) shows it at 0.047 uF. Go figure.
In the end, a well made cap will do fine. My belief is that 8 uF is excessive. The tube can't hope to be loaded that far down and put out a useable signal. 1 uF is overkill, better capacitors are available in this size.
Film / foil ? Personal preference.
-Chris
Edit: Hi Ken. Now that you mention it, you have been missing. I just thought you didn't see anything worth commenting on. Yes, some people get all freaked over the oddest topics. Life and death stuff tends to get my attention. High voltage, possible flames, plasma - that kind of stuff.
I'm just trying to recuperate enough to get your Lux back on the bench and possibly put the other power cord back.
One schematic (SA-5) shows the RIAA coupling cap at 8 uF, the other (5.1) shows it at 0.047 uF. Go figure.
In the end, a well made cap will do fine. My belief is that 8 uF is excessive. The tube can't hope to be loaded that far down and put out a useable signal. 1 uF is overkill, better capacitors are available in this size.
Film / foil ? Personal preference.
-Chris
Edit: Hi Ken. Now that you mention it, you have been missing. I just thought you didn't see anything worth commenting on. Yes, some people get all freaked over the oddest topics. Life and death stuff tends to get my attention. High voltage, possible flames, plasma - that kind of stuff.
I'm just trying to recuperate enough to get your Lux back on the bench and possibly put the other power cord back.