hi,
This is my first attempt at building a Tube Amp.
I just finished assembly of my Tubelab SE amp. Did all checks for final checkup based on information from George's web site. Everything went ok . However when I came to adjusting bias current I put in 45 tubes and then connected meters to adjust Bias current. I did not get any readings on both channels. Meters were showing 0.1 to 0.2 mA which I believe is basically zero current. I still went ahead and connected a line source. All I could hear was sound so feeble that I could only hear it if I put my ear pressed to the speaker. 45 tubes do not show any glow and are not hot. Could it be my 45 tubes? I got them from an Antique radio flea market. My tube tester does not support 4 pin tubes so I cannot test the tubes. What else should I do to check what is wrong? CCS IC are cold too. (Yes I do touch heat sink after power is turned off). What measurements and where I should take them to find out if circuit is working? I would be grateful for any guidance.
best regards,
This is my first attempt at building a Tube Amp.
I just finished assembly of my Tubelab SE amp. Did all checks for final checkup based on information from George's web site. Everything went ok . However when I came to adjusting bias current I put in 45 tubes and then connected meters to adjust Bias current. I did not get any readings on both channels. Meters were showing 0.1 to 0.2 mA which I believe is basically zero current. I still went ahead and connected a line source. All I could hear was sound so feeble that I could only hear it if I put my ear pressed to the speaker. 45 tubes do not show any glow and are not hot. Could it be my 45 tubes? I got them from an Antique radio flea market. My tube tester does not support 4 pin tubes so I cannot test the tubes. What else should I do to check what is wrong? CCS IC are cold too. (Yes I do touch heat sink after power is turned off). What measurements and where I should take them to find out if circuit is working? I would be grateful for any guidance.
best regards,
Evenharmonics, thanks for your reply. I think I was not correct in all the details that I listed in my original post (Inexperience shows 
isn;t it? Anyway, here is what I did.
1. Measured B+ at R30. B+ was high around 350V. I figured I will bring it down later lowering value of C4. I am using a choke in place of R4 resistor. I am using Hammond 270HX with 550VCT.
2. I think I did not properly check filament voltage. Initially I was sure I measured it around 3V but now I am not so sure. I tried many different things and my memory now got a little fuzzy about the exact number.
3. B- was about 178V.
4. I put voltmeters for grids of output tubes across R12 and R23 and set bias for most negative voltage. If I remember right it was about -67v.
5. I put meters at plates of 5842 and adjusted voltages close to 175V. (with 5842 tubes in).
6. Connected speakers and tried to adjust bias. Meters did not show any current. Sorry about a silly question but I am assuming voltmeter is to be set to measure mA current for this. Readings came out about 0.1mA and 0.2mA for each channel. When I adjusted bias pots there was hardly any chnage in current.
7. Checked with a line source in. I can barely hear sound from speakers. Had to put my ear to the speaker to notice any sound.
45 tubes do not glow or get hot. In my original post I said CCS is not getting hot. That is not true I mistakingly refered to U1 (5A current regulator) as CCS.
Now here is new info:
I checked signal path. I have good amplified signal right after 0.22 Coupling caps. It tells me all is good upto 5842 tubes. I put the lead of my signal tracer (a cheap headphone) past 2SK2700 and got signal there. I then moved up and touched the lead at grid of 45 tube and POOF !! smell of burning. It was instantaneous and sound is gone. I turned power off waited for circuit to be safe and then checked R34 (100 ohm) and now it is open. Surprisingly 45 tube was hot. Looks like I blew it up too. Hopefully these are the only two things that are toast . Well lesson learned.
One more thing before this blow up, I checked voltage before and after 5A current regulator (U1) and did not get right voltage. No 2.5 V after regulator. No -4 Volt before it. I am beginneing to suspect that 45 were not getting proper filament supply and something is wrong with D1 diode or U1 (5A regulator). I will replace both to see what happens.
One last thing. I am a little confused about how to isolate D1 and U1 from heatsinks. Are they both have to have their bodies electrically insulated from heatsinks? Is U1's body authomatically grounded on circuit board or do I have to make sure it is grounded? I did follow George's instructions for physically installaing them but am not sure if the source of my troubles lie there.
I apologize for such long post but I am all enbthusiatic about this project despite this setback which I am sure can be overcome with help from all the knowledgeable and helpful members like you.
best regards,
humayun
isn;t it? Anyway, here is what I did. 1. Measured B+ at R30. B+ was high around 350V. I figured I will bring it down later lowering value of C4. I am using a choke in place of R4 resistor. I am using Hammond 270HX with 550VCT.
2. I think I did not properly check filament voltage. Initially I was sure I measured it around 3V but now I am not so sure. I tried many different things and my memory now got a little fuzzy about the exact number.
3. B- was about 178V.
4. I put voltmeters for grids of output tubes across R12 and R23 and set bias for most negative voltage. If I remember right it was about -67v.
5. I put meters at plates of 5842 and adjusted voltages close to 175V. (with 5842 tubes in).
6. Connected speakers and tried to adjust bias. Meters did not show any current. Sorry about a silly question but I am assuming voltmeter is to be set to measure mA current for this. Readings came out about 0.1mA and 0.2mA for each channel. When I adjusted bias pots there was hardly any chnage in current.
7. Checked with a line source in. I can barely hear sound from speakers. Had to put my ear to the speaker to notice any sound.
45 tubes do not glow or get hot. In my original post I said CCS is not getting hot. That is not true I mistakingly refered to U1 (5A current regulator) as CCS.
Now here is new info:
I checked signal path. I have good amplified signal right after 0.22 Coupling caps. It tells me all is good upto 5842 tubes. I put the lead of my signal tracer (a cheap headphone) past 2SK2700 and got signal there. I then moved up and touched the lead at grid of 45 tube and POOF !! smell of burning. It was instantaneous and sound is gone. I turned power off waited for circuit to be safe and then checked R34 (100 ohm) and now it is open. Surprisingly 45 tube was hot. Looks like I blew it up too. Hopefully these are the only two things that are toast
. Well lesson learned.One more thing before this blow up, I checked voltage before and after 5A current regulator (U1) and did not get right voltage. No 2.5 V after regulator. No -4 Volt before it. I am beginneing to suspect that 45 were not getting proper filament supply and something is wrong with D1 diode or U1 (5A regulator). I will replace both to see what happens.
One last thing. I am a little confused about how to isolate D1 and U1 from heatsinks. Are they both have to have their bodies electrically insulated from heatsinks? Is U1's body authomatically grounded on circuit board or do I have to make sure it is grounded? I did follow George's instructions for physically installaing them but am not sure if the source of my troubles lie there.
I apologize for such long post but I am all enbthusiatic about this project despite this setback which I am sure can be overcome with help from all the knowledgeable and helpful members like you.
best regards,
humayun
More Development in the build
Here is an update.
Amp seems to be working now after I repalced the resistor I fried, but I have a strange problem. Only one channel works at a time. If I plug in both 45 tubes output drops and filament voltage also drops to about 1.2V. If I remove one 45 tube amp comes alive with full output and full filament voltage 2.5V. It happens with either of the channels. Whuch tells me that circuit wise each channel is put together ok. I am using a pretty thin jumper wire for my jumper from Pad 1 to Pad 4. Can that be the reason that with both 45 tubes it limits juice flow? It is late but tomorrow morning I am going to repalce that jumper and check what happens. Another problem I am having is that my B+ is running very high. My B+ is about 414V . I have played with C4 (reduced it from 47uf to 4.7uf ) with no success in bring B+ down. I am using a choke already. My transformer is Hammond 270HX. Is using this transformer a mistake? Should I switch to one with lower voltage? For selection of this transfromer I used George's instructions for a universal amp on his web page.
My B- is also very high (over 200v). My line volatge is about 122V.
I would appreciate any help and pointers. Despite these setbacks I am enjoying every minute of working on this amp. Hopefully I would be able to get it going.
thank you.
Here is an update.
Amp seems to be working now after I repalced the resistor I fried, but I have a strange problem. Only one channel works at a time. If I plug in both 45 tubes output drops and filament voltage also drops to about 1.2V. If I remove one 45 tube amp comes alive with full output and full filament voltage 2.5V. It happens with either of the channels. Whuch tells me that circuit wise each channel is put together ok. I am using a pretty thin jumper wire for my jumper from Pad 1 to Pad 4. Can that be the reason that with both 45 tubes it limits juice flow? It is late but tomorrow morning I am going to repalce that jumper and check what happens. Another problem I am having is that my B+ is running very high. My B+ is about 414V . I have played with C4 (reduced it from 47uf to 4.7uf ) with no success in bring B+ down. I am using a choke already. My transformer is Hammond 270HX. Is using this transformer a mistake? Should I switch to one with lower voltage? For selection of this transfromer I used George's instructions for a universal amp on his web page.
My B- is also very high (over 200v). My line volatge is about 122V.
I would appreciate any help and pointers. Despite these setbacks I am enjoying every minute of working on this amp. Hopefully I would be able to get it going.
thank you.
Conclusion. TSE working
I am happy to report that problem is solved and both channels of TSE are working great. It was my thin choice of jumper between PAD1 and PAD4 which was messing things up. I put a temporary heavy wire jumper and everything worked. Filament volatreg is now close to 2.5V and both channels are working with beautiful sound.
I still have high B+ and B-. B+ = 347V and B- = -212V. B+ was even higher over 370V but I managed to lower it by using 125V tap of the transformer instead of 115V tap. I still want to lower it. I am down to 4.7uf for C4. I will probably replaced my choke (Hammond 193B, 155ohm) with higher resistance choke to see what happens.
best regards,
humayun
I am happy to report that problem is solved and both channels of TSE are working great. It was my thin choice of jumper between PAD1 and PAD4 which was messing things up. I put a temporary heavy wire jumper and everything worked. Filament volatreg is now close to 2.5V and both channels are working with beautiful sound.
I still have high B+ and B-. B+ = 347V and B- = -212V. B+ was even higher over 370V but I managed to lower it by using 125V tap of the transformer instead of 115V tap. I still want to lower it. I am down to 4.7uf for C4. I will probably replaced my choke (Hammond 193B, 155ohm) with higher resistance choke to see what happens.
best regards,
humayun
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