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Possible Power Transformer problem

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I finally got around to building the second TSE board. On the previous board I ran a 10 watt resistor for R6 and it got so hot it toasted the pads and C7. On the previous board I used a second switch to power the HV supply and a main switch for everything else. I believe my wife was listening and left one of the switches on for an number of days.

That said I can leave all tubes out and get correct -volts on R30 and checking T1 through T8 all look good.

With a rectifier tube in I only get around 50 volts across R30 and I and hear a very muted snap (almost like a relay kicking in) and profound plastic/wax melting smell until I shut it down. I cannot trace the source of the heat from the board or components on the board. Filament supply for the Rectifier, output tubes and the 5842 seems good.

I cannot measure any thing across R29 and R18.

I Start my work week tomorrow and I have been at this all day so I may take awhile to do further tests. Thanks in advance for any insight.
 
That said I can leave all tubes out and get correct -volts on R30 and checking T1 through T8 all look good.

R30 is the 130K bleeder resistor in the B+ line? I would think you should get zero at that point with no tube installed.

With a rectifier tube in I only get around 50 volts across R30 and I and hear a very muted snap (almost like a relay kicking in) and profound plastic/wax melting smell until I shut it down.

Check value and integrity of resistor R30, and filter capacitors C4 and C5.

Win W5JAG
 
I actually get around a negative 260-275 volts across R30 with not rectifier.

I will check R30 and the c4 and c5 caps when I get home, I am reusing a 2.7uF mundorf supreme for c4 and had to run leads to it so may be suspect. I have a brand new C5 Panasonic 470uF with two 40uF oil caps added.
 
Just remembered I am running a inrush current limiter and it may be getting hot. I used to run a second limiter for the H.V. tap on the power transformer. This could be the source of the sound I am hearing.
The best place for the current limiter would probably be the H.V. tap slowing B+ from the 5U4G.
 
Still getting the ticking sound when powering up with a rectifier even after removing the current limiter
Nothing on this board shows sign of arcing or overheating.

When wiring in the led pilot lamp i accidentally brushed across the leads of the IEC outlet with a screw driver and the fuse popped but I did not give it much thought. Is it possible the 20amp on/off switch or IEC receptacle has been compromised?


I may have to get a cap tester, one that will test caps in circuit would be of great help now. R30 looks good. When I built this board I put all resistors in individual drawers of a small parts unit after testing them and tested them again before installation.

I will replace C4 with another poly cap when I get a chance.
 
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Ticking is coming from the IEC receptacle, the one I popped a fuse in. I talked to one of the engineers at Edcor and wanted to rule out the Transformer and he indicated he never ran across one that had good static numbers and acted different under load.
I ordered a new C5 cap and a 130k resistor for R30.
I run the Moto Guzzi motorcycle section of a business and there is a saying about Guzzi that goes...." Moto Guzzi, making mechanics out of owners since 1921."
I fell here the same could be said about Tubelab. I say that without any malice towards Tubelab. It truly is a wonderful product.
 
At one point, I had four Jaguars, when you really did need two to make sure you had one you could drive, and was proficient enough at repairing them that other professional people were bringing their Jags to me to fix.

I bought my wife a new one in 2004, and it hasn't required any repairs at all - still has the factory battery. I would like to get her a new one, but the old one is still like new -only has about 40K miles on it. When I bought her that car, I REALLY wanted to get her a Quattroporte, but I chickened out - didn't feel up to the learning curve, after figuring out the Jaguar systems.

I still keep a 12 cylinder Jag around for when I want a couple of sets of bloody knuckles, and need to burn a gallon of premium every eleven miles or so.

Win W5JAG
 
In the late seventies there was a guy living in the same apartment comples as I that had a XKE I believe-12cyl. I left in the early AM one Sunday morning for a motorcycle ride and he was outside doing a valve adjustment. I got back shortly before dark and he was buttoning up with bloody knuckles. At least you are not alone
 
But Jag's are pretty

IMG_5338.jpg


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OK, I replaced C4, C5 and R30 (with the diode) and the checkout numbers look good. B+ is a little high from previous but OK. I am getting:
304-307 B+
Neg across R7 -162
5842 came right up and settled in 175v
bias for output tubes all works good set at 28mA
My problem is the choke now hums. If I turn down the output tube bias (45's) the hum drops accordingly. I am using an ElectraPrint 10-15 uH choke, this amp was dead tomb quiet before.
Two changes since building this board are I changed R14 and R25 to 20K instead of 30K and I installed a LED pilot lamp inline with the back of the IEC plug for the power cord to the on/off switch. I forgot one other thing is I used a 4.7uF cap for C4 instead of a 20uF cap used previously.
I have not hooked up to speakers yet, the choke can be heard humming away and can be felt from the board when adjusting the output tube bias through the screw driver used to adjust the pot.
 
I went through and made sure of solder connections, removed the choke and pulled off the bell covers and nothing looked smoked or hot. I soldered the leads for the choke in opposite holes from the firs time. Set bias and rechecked 5842 voltage. I used a cheater plug and make sure I did not have any current leaking to ground. The amp was quiet.

Brought it upstairs and made music. Eventually the hum returned, I tapped the choke and hum went away. This happened a number of times until the hum came and stayed.

I read another post where someone swapped the power transformer secondaries and hum went away.

This hum is audible during quiet passages and no music playing. You do not have to strain to hear it.
 
I removed the choke and installed a 150ohm resistor and hum still persists. Will hum with the 5842 tubes removed. I do not know why tapping on the choke made the hum go away before unless that tap exposed a problem elsewhere like the power transformer or a cold solder joint.
All the secondaries on the pwr transformer are correct and I talked to Edcor last week and they indicated it would be highly unusual for a bad prw transformer it the secondaries are good.

Getting frustrated and way above my head.
 
Have you added any new components in the system? Maybe you have a ( dreaded ) ground loop that has started.

It doesn't surprise me it would hum with a resistor in place of the choke.

It's possible you replaced bad capacitors with bad capacitors. I've done that before. It's also possible that choke was ( is ) bad. I'm not sure how to check for a bad choke, other than to sub in a known good one. Maybe someone else could give some insight.

Win W5AJG
 
Hi Win,
It's not that it hums with the resistor, it has not seemed to change. I assumed it was the choke since on and around the choke at one time made the hum go away (not now).

I am back thinking power transformer because of the clicking I used to hear. Adding a CL-140 termistor stopped the clicking because the slow startup of HV secondary.

I already eliminated ground loops as a problem.

I talked to Jack at Electra Print and he gave instructions to check the choke and everything seems good there.

Jack said to take readings on the pwr transformer secondaries while the amp is under load. Just got back from the gym and store and prepping for the snow tomorrow.
 
HI all,
The choke wires are away from input/output. Same setup I had before except with this new board I have hum, this same amp was dead quiet.

The source is not a factor and neither is ground loops. Hums with nothing connected to input - both channels. Again hum is there without the 5842's connected.

On the previous board I used Riken-Ohm carbon film caps for grid stoppers for the 5842's and 45's. This amp I am using Ohmite carbon comps on the 5842 and Dale RN60's (metal film) on the 45's.
 
Spent time with the amp downstairs with the amp cleaning up wiring and reflowing again.
I measured the secondary's under load and the only alarming number was the 6.3 volt tap is reading 7.2 volts. I did not check the 5842's but the 45 heater voltage is spot on.

With the amp on the bench without any input connected I am getting 24-25 mV (.024 volt a/c measured on my DVM) out of both channels. I am running the amp into 8 ohm power resistors. It is enough that the sound can be heard coming from the Electra Print output transformers. No vibration can be felt but I can hear the transformers singing quietly.
 
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