Allied now lists them as "Allied by Hammond" in their catalog and "Hammond Manufacturing" on the web site. This is in contrast to the 80's catalog that listed them as "Allied's own" tube amp power transformers. The transformer shown in the picture on the web site has 2004 date on it, same as the one in my SSE.
I just removed the board from the chassis to replace C3 (just in case) and I noticed that R3 was lighter blue the the rest of the resistors, and there are signs of heat on the PCB in that location.
Lifted a leg of R3 and tested - infinite resistance.
So I'll have to try to find a replacement for that now, too.
If I can't find a 1w 10k resistor, can I parallel 4 quarter-watt w 39k ohm resistors in there, for 9750 ohms and call it fugly but good enough?
Lifted a leg of R3 and tested - infinite resistance.
So I'll have to try to find a replacement for that now, too.
If I can't find a 1w 10k resistor, can I parallel 4 quarter-watt w 39k ohm resistors in there, for 9750 ohms and call it fugly but good enough?
Last edited:
Thanks George.
I'll go with the 3w part and put it on the back of the board this time, beside C3.
I either ran out of or lost my solder wick, so these repairs are going to be ugly. I have a solder sucker but it can only get the bulk.
I hate the idea of re-flowing the old solder and then poking leads through the liquid, but I don't have much choice right now.
I'll go with the 3w part and put it on the back of the board this time, beside C3.
I either ran out of or lost my solder wick, so these repairs are going to be ugly. I have a solder sucker but it can only get the bulk.
I hate the idea of re-flowing the old solder and then poking leads through the liquid, but I don't have much choice right now.
Last edited:
I just modeled the setup in PSUD2 and maybe it makes sense.
My mains AC is 120V, and the primary on the 6K7VG is 117V. Some quick math tells me that this pushes the nominal secondary voltage from 375-0-375 to 385-0-385 (after rounding).
When you use PSUD2's Off-Load Voltage Calculator and plug in 385V as the nominal voltage, it calculates an off-load voltage of 404V.
With the simulation configured this way and a 120mA load, the voltage at the load is 469V.
I can throw a 5U4GB in to bring the B+ down a bit (PSU2 calculates 435V, actually), but what else can I do?
My mains AC is 120V, and the primary on the 6K7VG is 117V. Some quick math tells me that this pushes the nominal secondary voltage from 375-0-375 to 385-0-385 (after rounding).
When you use PSUD2's Off-Load Voltage Calculator and plug in 385V as the nominal voltage, it calculates an off-load voltage of 404V.
With the simulation configured this way and a 120mA load, the voltage at the load is 469V.
I can throw a 5U4GB in to bring the B+ down a bit (PSU2 calculates 435V, actually), but what else can I do?
Last edited:
I ran a few more tests with various tube combinations. Maybe the results will provide some clues to George or the others what might be wrong.
1) 5AR4 alone = 485-490V B+ and I usually kill it at 490V
2) 5U4-GB alone = B+ levels out at 470-ish volts
3) 5AR4 + 12AT7 + any power tubes (tried a pair of EL34 and a pair of 6P3S-E) = ~ 220V B+
4) 5U4-GB (two different samples) + 12AT7 + any power tubes as above = B+ rises to ~460V and then immediately starts to drop back down rapidly (and I shut it off as soon as it starts dropping).
So I am right back to where I was months ago.
1) 5AR4 alone = 485-490V B+ and I usually kill it at 490V
2) 5U4-GB alone = B+ levels out at 470-ish volts
3) 5AR4 + 12AT7 + any power tubes (tried a pair of EL34 and a pair of 6P3S-E) = ~ 220V B+
4) 5U4-GB (two different samples) + 12AT7 + any power tubes as above = B+ rises to ~460V and then immediately starts to drop back down rapidly (and I shut it off as soon as it starts dropping).
So I am right back to where I was months ago.
Last edited:
Dim bulb tester will result in low voltages as it limits current. Bulb should be lit as current is flowing but not too brightly.
My 375-0-375 Hammond results in 420V B+ with 5AR4 rectifier with all tubes installed. With SS rectifiers it is more like 440V
Unloaded without the bulb tester max voltage could be around 375*1.4=525v but the CL90 and tube rectifier should slow things enough at startup that it should just go to operating voltage without overshoot.
Always have a load hooked up (resistor or speakers) when powering up the tube amp. Probably you know that!
One last thing. Careful with the 5U4GB as yes it has greater voltage drop but warmup is very fast so startup voltages will be higher than the 5AR4.
My 375-0-375 Hammond results in 420V B+ with 5AR4 rectifier with all tubes installed. With SS rectifiers it is more like 440V
Unloaded without the bulb tester max voltage could be around 375*1.4=525v but the CL90 and tube rectifier should slow things enough at startup that it should just go to operating voltage without overshoot.
Always have a load hooked up (resistor or speakers) when powering up the tube amp. Probably you know that!
One last thing. Careful with the 5U4GB as yes it has greater voltage drop but warmup is very fast so startup voltages will be higher than the 5AR4.
Last edited:
With the tester. I need to watch for runaway conditions that could fry stuff. There is something seriously wrong with this amp and I am sure it will burn out this brand new transformer if I am not careful. I have been through this before (months ago).
I can't see how a dim bulb tester would cause the disparity between test #3 and #4.
Test #3 = 220v B+ with very little glow on the tester (barely visible)
Test #4 = B+ rises to 460v normally and then immediately crashes (rapidly drops), with medium glow on the tester.
I can't see how a dim bulb tester would cause the disparity between test #3 and #4.
Test #3 = 220v B+ with very little glow on the tester (barely visible)
Test #4 = B+ rises to 460v normally and then immediately crashes (rapidly drops), with medium glow on the tester.
Last edited:
What wattage bulb do you have in your tester?
The rectifier will warm up faster than the output tubes. That's why the B+ shoots up. As the output tubes warm up they start to draw current which is limited by the light bulb, hence the drop in B+. This is normal. The output tubes will eat about 25 watts each in normal operation and the rectifier eats 10 to 15 just to light the heater. They are splitting the applied line voltage with the light bulb so the neither one gets full power.
490 volts with no other tubes is probably normal. My amp goes over 500 volts at first power on with a 5AR4 and no bulb tester. It drops to 430 - 440 once everything is operating depending on line voltage. Nothing blew up when 490 volts happened which is good.
You state that with all tubes in place, the B+ drops to about 218 volts. This might be normal, it depends on the characteristics of your light bulb. Did you try to play music under these conditions? If not, try it. You should get something resembling sound, it will be weak and distorted, but if both channels make noise, all may be normal.
Removing one output tube should get you more B+ voltage, and maybe enough to get better sound out of the channel with an output tube. If so take out the remaining tube and put back the one you previously pulled. If that channel works better the amp is probably ready for a full test without the bulb. Just make sure that you have a good 2 amp fuse in place.
The rectifier will warm up faster than the output tubes. That's why the B+ shoots up. As the output tubes warm up they start to draw current which is limited by the light bulb, hence the drop in B+. This is normal. The output tubes will eat about 25 watts each in normal operation and the rectifier eats 10 to 15 just to light the heater. They are splitting the applied line voltage with the light bulb so the neither one gets full power.
490 volts with no other tubes is probably normal. My amp goes over 500 volts at first power on with a 5AR4 and no bulb tester. It drops to 430 - 440 once everything is operating depending on line voltage. Nothing blew up when 490 volts happened which is good.
You state that with all tubes in place, the B+ drops to about 218 volts. This might be normal, it depends on the characteristics of your light bulb. Did you try to play music under these conditions? If not, try it. You should get something resembling sound, it will be weak and distorted, but if both channels make noise, all may be normal.
Removing one output tube should get you more B+ voltage, and maybe enough to get better sound out of the channel with an output tube. If so take out the remaining tube and put back the one you previously pulled. If that channel works better the amp is probably ready for a full test without the bulb. Just make sure that you have a good 2 amp fuse in place.
Thanks George.
Once again I am displaying my almost complete ignorance of electronics/electricity. I'll leave it at that for now, regarding the light bulb - except to say it is a 100w "industrial strength" bulb, purchased because that was literally the only incandescent bulb I could buy at my local Home Depot. Had to buy a 2-pack, of course, for a ridiculous price. Although nothing compared to this insanity Incandescent Light Bulbs | DelMarFans.com
I did not try playing music during any of the tests. I simply watched the DMM readout and the light bulb and pounced on the power bar when things seemed wrong. My anxiety level is about 7 out of 10 when I am performing these tests.
I will do as you say; hook up a source and see if I can get music, and then remove a power tube, then swap in the other one, etc. and report back.
Once again I am displaying my almost complete ignorance of electronics/electricity. I'll leave it at that for now, regarding the light bulb - except to say it is a 100w "industrial strength" bulb, purchased because that was literally the only incandescent bulb I could buy at my local Home Depot. Had to buy a 2-pack, of course, for a ridiculous price. Although nothing compared to this insanity Incandescent Light Bulbs | DelMarFans.com
I did not try playing music during any of the tests. I simply watched the DMM readout and the light bulb and pounced on the power bar when things seemed wrong. My anxiety level is about 7 out of 10 when I am performing these tests.
I will do as you say; hook up a source and see if I can get music, and then remove a power tube, then swap in the other one, etc. and report back.
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.