Hey all, While I am finaly getting underway on the Quicksilver 8417 Clone amp I am building (only took me two years to plan) I saw a Golden Tube Audio SE-100 for sale locally, so I bought it (don't tell the wife).
This amp was laying around for years and had a layer of dust and crud all over it. I lugged it al the way home (all 80 pounds of it) and cleaned it off. Blew out the amp chassis with compressed air and wiped it down. I then wiped off the EL34 tubes (10 in all, one drivers and the other four are paralleled - per channel). I tested them on my tube tester and they were all in the high 90%. They are Electro Harmonix.
The input tube was a 6SL7 I think (no markings). and tube tester said it was fine too.
Anyway brought it up on the variac and zeroed the bias pots. One tube started red plating, and was reading over 1.9v (supposed to be biased to 450mv). Yikes!...Shut it down and worked the bias pots back and forth for a few minutes - did the same to all the other pots. Started back up and all was ok...bias up to 350mv for 5 min, then 400mv for another 5 min, then on to 450mv (actually says to bias to 500mv, but I will leave it at 450mv)
Anyway, put it on a pair of B&W DM 220 (my beaters) and sounded good, but had a bad hum that was clearly audible with cd paused. Also had a ton of gain.
I found the schematic (attached - don't know if correct) and it listed the input tube as a 6SN7, so I swapped it and gain lower and hum went down considerably... still need to do some critical listening...not a bad sounding amp. I like.
Anyway a couple questions.
This amp is listed as 100 watts, class AB Push Pull - Huh? Its Single ended paralleled, like its little brother the SE-40. ..and aren't all Single Ended parallel amps class A?
Also, what is the "correct" tube for input - 6SL7 or 6SN7? Quite happy with the 6SN7 in that spot...
Pics later...
This amp was laying around for years and had a layer of dust and crud all over it. I lugged it al the way home (all 80 pounds of it) and cleaned it off. Blew out the amp chassis with compressed air and wiped it down. I then wiped off the EL34 tubes (10 in all, one drivers and the other four are paralleled - per channel). I tested them on my tube tester and they were all in the high 90%. They are Electro Harmonix.
The input tube was a 6SL7 I think (no markings). and tube tester said it was fine too.
Anyway brought it up on the variac and zeroed the bias pots. One tube started red plating, and was reading over 1.9v (supposed to be biased to 450mv). Yikes!...Shut it down and worked the bias pots back and forth for a few minutes - did the same to all the other pots. Started back up and all was ok...bias up to 350mv for 5 min, then 400mv for another 5 min, then on to 450mv (actually says to bias to 500mv, but I will leave it at 450mv)
Anyway, put it on a pair of B&W DM 220 (my beaters) and sounded good, but had a bad hum that was clearly audible with cd paused. Also had a ton of gain.
I found the schematic (attached - don't know if correct) and it listed the input tube as a 6SN7, so I swapped it and gain lower and hum went down considerably... still need to do some critical listening...not a bad sounding amp. I like.
Anyway a couple questions.
This amp is listed as 100 watts, class AB Push Pull - Huh? Its Single ended paralleled, like its little brother the SE-40. ..and aren't all Single Ended parallel amps class A?
Also, what is the "correct" tube for input - 6SL7 or 6SN7? Quite happy with the 6SN7 in that spot...
Pics later...
Last edited:
Hi John,
The amplifier is actually push-pull and not single ended. But it is unconvential as the output tubes are cathode loaded thus supplying current to the signal amplitude to provide rated power. The high voltage positive is at ground and the negative is elevated. Also, the screens are coupled through the output transformer, but I wonder if there is a drawing error because they are connected asymmetrically. I would think the C-T (#5) should be at ground. Phase inversion for P-P is by way of the coupling/driver transformer at the upper left. Anyway, if the schematic says 6SN7 and it seems to work better, then that's the one to use.
The amplifier is actually push-pull and not single ended. But it is unconvential as the output tubes are cathode loaded thus supplying current to the signal amplitude to provide rated power. The high voltage positive is at ground and the negative is elevated. Also, the screens are coupled through the output transformer, but I wonder if there is a drawing error because they are connected asymmetrically. I would think the C-T (#5) should be at ground. Phase inversion for P-P is by way of the coupling/driver transformer at the upper left. Anyway, if the schematic says 6SN7 and it seems to work better, then that's the one to use.
OK, cool. Thanks for the explanation...
Hmm, I put in a cheater plug and the hum has all but gone...I even tried the 6SL7 and all gone too...
Hmm, I put in a cheater plug and the hum has all but gone...I even tried the 6SL7 and all gone too...
By cheater plug do you mean one that lifts the chassis safety ground thereby removing a ground loop? Try not to leave things this way if at all possible because you are defeating an important personal safety feature. Perhaps the filter caps need more time to reform. And I'm wondering if the model number SE-100 made you assume it was single ended. SE could mean other things like special edition, signature edition or super expensive. 😀
Yes, the cheater plug lifts the amp safety ground. Not the way I would like to leave it either...
The SE apparently does not mean Single ended...The SE-40 does I believe...The SE-100 nice sounding amp - but a crazy circuit.
The 6SL7 still has this weird random noise - like very soft popping. With 6SN7 not really noticeable as the gain is much lower.
The SE apparently does not mean Single ended...The SE-40 does I believe...The SE-100 nice sounding amp - but a crazy circuit.
The 6SL7 still has this weird random noise - like very soft popping. With 6SN7 not really noticeable as the gain is much lower.
Would you happen to have a manual for this amp?
I see the bias pots on the top, but where are the bias test points to measure the voltage?
Hum in this amp
I'm very familiar with this amp and you cant get rid of all of the hum because it is coming from the transformer coupling and it's more of a buzz. You don't really hear the buzz when it's playing but this is different than your probem right now which also causes hum..
Now, keep in mind the SE100 works in a very unique way. On a typical tube amp, we supply positive DC to the plate and Screen grid, negative voltage at the control grid and we ground the cathode thru an 11 ohm resistor lets say.
This amp puts the high voltage B- supply on the cathode and SG, a positive DC on the on the control grid, we ground the plate thru an 11 ohm resistor.
The amp is Push Pull but what goes bad on the SE100s are the small coupling or bypass caps. They had a tendency to short so you pull the board out and check all the caps on the board with the EL34s with an ohmmeter and you will no doubt find the culprit cap.
I'm very familiar with this amp and you cant get rid of all of the hum because it is coming from the transformer coupling and it's more of a buzz. You don't really hear the buzz when it's playing but this is different than your probem right now which also causes hum..
Now, keep in mind the SE100 works in a very unique way. On a typical tube amp, we supply positive DC to the plate and Screen grid, negative voltage at the control grid and we ground the cathode thru an 11 ohm resistor lets say.
This amp puts the high voltage B- supply on the cathode and SG, a positive DC on the on the control grid, we ground the plate thru an 11 ohm resistor.
The amp is Push Pull but what goes bad on the SE100s are the small coupling or bypass caps. They had a tendency to short so you pull the board out and check all the caps on the board with the EL34s with an ohmmeter and you will no doubt find the culprit cap.