Hi Guys,
I was looking for a cheap pre for a chipamp that I had recently built, and wanted to try a tube version to see what they were like, so I took a chance on one of the cheap Chinese options on EBay. I got a version that was supposed to be based on the Matesse Atom that uses two 6N3 tubes for about 50 bucks shipped including the transformer. It looks to be put together nicely and the board seems to be of pretty good quality, but the tubes that came with it look really cheap. Well the bottom line is that it doesn't work. When hooked up I get a very faint sound coming out with the volume turned all the way up. I checked out things a bit with my DMM. The transformer is fine, with 115 vac it gives 227 vdc and 7.7 vdc after rectification with no load. The dodgy green led's under the tubes light up and the tubes glow very dimly inside, but don't get even warm. I tested the vdc on the tube pins and the results are in the attached pic. I don't know a thing about tubes being a SS guy. I'd appreciate any advice on how to proceed to get this thing working.
Thanks,
PJN
I was looking for a cheap pre for a chipamp that I had recently built, and wanted to try a tube version to see what they were like, so I took a chance on one of the cheap Chinese options on EBay. I got a version that was supposed to be based on the Matesse Atom that uses two 6N3 tubes for about 50 bucks shipped including the transformer. It looks to be put together nicely and the board seems to be of pretty good quality, but the tubes that came with it look really cheap. Well the bottom line is that it doesn't work. When hooked up I get a very faint sound coming out with the volume turned all the way up. I checked out things a bit with my DMM. The transformer is fine, with 115 vac it gives 227 vdc and 7.7 vdc after rectification with no load. The dodgy green led's under the tubes light up and the tubes glow very dimly inside, but don't get even warm. I tested the vdc on the tube pins and the results are in the attached pic. I don't know a thing about tubes being a SS guy. I'd appreciate any advice on how to proceed to get this thing working.
Thanks,
PJN
Attachments
Both anodes get 224V, that's OK but what about the rest? Circuit please. Please measure pins 8 & 2 (cathodes).
Hi Horntube,
I measured the sockets the first time by placing the negative lead of the DMM at the negative rectifier dc outlet and touching the positive lead to each pin. I'm guessing to measure the cathode I need to reverse the procedure and put the positive DMM lead on the rectifier + dc out. When I did that every pin except 4 and 6 measured 224 vdc. 6 & 4 were 0.
PJN
I measured the sockets the first time by placing the negative lead of the DMM at the negative rectifier dc outlet and touching the positive lead to each pin. I'm guessing to measure the cathode I need to reverse the procedure and put the positive DMM lead on the rectifier + dc out. When I did that every pin except 4 and 6 measured 224 vdc. 6 & 4 were 0.
PJN
Ok, I measured all of the pins against the ground plane. With the negative lead of the DMM on the ground plane I get 224 vdc on pins 4 and 6 as shown in the diagram above, I get 0 vdc on all of the other pins. Unfortunately as of yet I have been unable to get a schematic, I'll email the seller to see if he has one. I've attached an pic of the underside of the board, the out RCA's are in the upper left, notice the two spots for smd resistors that are empty. On the input RCA there are smd's there.
Attachments
Pic is not very good but if the SMD's R9, 10, 15 & 17 are missing than you have to put some resistors in there! It can't work without cathode resistors, no wonder you measure 0V on the cathode pins.
Oh, just forgot to mention: Throw the Chinese 6N3 away and put some Soviet Red Army 6N3P in there and you will be amazed!
Well, not that much please!!!😉
An externally hosted image should be here but it was not working when we last tested it.
Well, not that much please!!!😉
Hello,
If the tubes are not hot take a look at the heater voltage. Between pins 1 and 9 there should be ~ 6 volts.
DT
All just for fun!
If the tubes are not hot take a look at the heater voltage. Between pins 1 and 9 there should be ~ 6 volts.
DT
All just for fun!
Hi DualTriode,
I measure 7.6 vdc between pins 1 & 9. Between 1&2, 1&3, 1&5, 1&7, and 1&8 get 0 vdc. Between 1&4, and 1&6 get 224 vdc.
Horntube,
There are smd resistors on R9, 10, 15 & 17.
Thanks for helping.
PJN
I measure 7.6 vdc between pins 1 & 9. Between 1&2, 1&3, 1&5, 1&7, and 1&8 get 0 vdc. Between 1&4, and 1&6 get 224 vdc.
Horntube,
There are smd resistors on R9, 10, 15 & 17.
Thanks for helping.
PJN
If this is the circuit...
then I don't think the missing resistors are needed as they are just parallel to the load. Might want to power down and check the resistance from the cathode pins (tubes removed) to ground an make sure that the resistors are not bridged by solder, open or poofed.
When powered up with tubes in place 3 and 8 should be a couple of volts and 2 and 7 should be zero. Clearly if you only have a couple of volts drop from B+ to the plates the tubes are not conducting for some reason as I doubt that we have 1k plate resistors. Also be sure the the socket pins are making good contact.
An externally hosted image should be here but it was not working when we last tested it.
then I don't think the missing resistors are needed as they are just parallel to the load. Might want to power down and check the resistance from the cathode pins (tubes removed) to ground an make sure that the resistors are not bridged by solder, open or poofed.
When powered up with tubes in place 3 and 8 should be a couple of volts and 2 and 7 should be zero. Clearly if you only have a couple of volts drop from B+ to the plates the tubes are not conducting for some reason as I doubt that we have 1k plate resistors. Also be sure the the socket pins are making good contact.
If there are no resistors at the cathodes it can't work. There MUST be some voltage on the cathodes - if not it can't work.
Hi Guys,
I was checking the cathode resistors (good), and sprayed the tube sockets with some contact cleaner and put the tubes in and out a couple of times before taking some powered up voltage reading as mashaffer had advised. When I powered up this time the tubes got hot, so I hooked it up and it is working. I'm guessing dirty tube sockets were the culprit all along.
I'm really impressed so far with the sound quality. The soundstage seems more 3D, everything is very clear and clean, vocals are very nice. It really improves the chipamp's presentation. Certainly 50 bucks well spent. I guess there is something to tubes after all. I think a tube amp project is in my future. Thanks again for all of your help.
PJN
I was checking the cathode resistors (good), and sprayed the tube sockets with some contact cleaner and put the tubes in and out a couple of times before taking some powered up voltage reading as mashaffer had advised. When I powered up this time the tubes got hot, so I hooked it up and it is working. I'm guessing dirty tube sockets were the culprit all along.
I'm really impressed so far with the sound quality. The soundstage seems more 3D, everything is very clear and clean, vocals are very nice. It really improves the chipamp's presentation. Certainly 50 bucks well spent. I guess there is something to tubes after all. I think a tube amp project is in my future. Thanks again for all of your help.
PJN
A tube preamp is the most important thing in a system. With a good sounding tube pre you are on the halfway to heaven. Good luck & enjoy it. Don't forget the 6N3P tubes I mentioned it is a huge step forward.
Getting different better quality tubes is tops on my agenda. I just ordered some J.A.N. GE 5670W to try. I'll look around for the Russian 6N3P versions too.
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