5e3 ( VHT Standard 12) voltages question after Sovtek --> JJ rectifier...

nickmm

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Still a little cool but safe.
Clip the extra filter and see if your plate voltage comes up a bit.
The JJs don't break up as early as the Tungsol/Mullard 6v6 or NOS. They are a bit grainier. You should be getting some grind at a reasonable volume.
I found the ideal tonal window in this style amp to be more narrow than the latter designs.
 

bluesholyman

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The JJs don't break up as early as the Tungsol/Mullard 6v6 or NOS. They are a bit grainier. You should be getting some grind at a reasonable volume.

I have the black glass Ruby's in here, which looks like EHX but may be chinese - flat top on the glass. I'll get a moment to clip that extra cap and check the others for their values a little later this afternoon or this evening, then re-measure the plate voltage and current.
 
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nickmm

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I have the black glass Ruby's in here, which looks like EHX but may be chinese - flat top on the glass. I'll get a moment to clip that extra cap and check the others for their values a little later this afternoon or this evening.
Don't stress about the tube differences. They should all come into the ballpark when the amp is running right.
 

bluesholyman

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Ok, the B+2 filter cap is reading .10 nF - yes, nano....seems it is effectively shot. I guess someone did a lazy fix and put that F&T there without removing the old one.....sigh.....looks like I'll will go ahead and swap them, now that I've snipped the F&T - hope the leads are still long enough, but amp is down for the moment....

I might just order 3 replacements at 16uF and go ahead and do them all - these filter caps are made by Jaguar - never heard of them.
 

Wally

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Ime, that is some very low plate voltage. At any rate, you are at 77.5% of MPD. I would expect a ’clean’ amp for a 5E3 if all else is working properly. I personally would be wondering why the B+ is so low? I have observed 350-360 in vintage 5E3s that were glorious amps.
 

bluesholyman

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Ime, that is some very low plate voltage. At any rate, you are at 77.5% of MPD. I would expect a ’clean’ amp for a 5E3 if all else is working properly. I personally would be wondering why the B+ is so low? I have observed 350-360 in vintage 5E3s that were glorious amps.
Possibly because of 470 ohm screen resistors on the power tubes that aren't on the standard 5e3 circuit - only a guess, really. Found that info here
 

Wally

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Possibly because of 470 ohm screen resistors on the power tubes that aren't on the standard 5e3 circuit - only a guess, really. Found that info here
It would be of interest pull the tubes and measure the voltages in that ‘unloaded’ status. I do not believe that the screen grid resistors would affect B+????
 

Wally

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At about 38 min a good explanation of the 470 ohm screens.


First, I would suggest that an educational video should show a person using a ’chopstick’ or some other non-conductive probe for the purpose he is using that screwdriver. I understand that this man knows tube circuits and that he has drained the caps, but that screwdriver just looks very much out of place when I see it probing into the circuit that way. So does a bare finger. I watched a fellow who is learning by reading and watching these videos, and I admit there is much to be learned in this type of video. However, I had to caution him about sticking his fingers down into a circuit and making contact with his finger as he was making some query or observational about his amp he had broguht by. one should never be lackadaisical about these dangers…especially during instruction. End of rant…..

As for the screen grid resistor vis-a-vis B+, that video doesn’t establish
any effect of that resistance and the screen grid current draw on the B+, does it?
 

Wally

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Also, I pers9nally do not understand why one would opt for a switched NFB loop resistance rather than use a potentiometer to sweep from The highest cancellation factor to any in a range of lower cancellation factors.
OMMV….obviously. I simply like versatility, and pot allows greater versatility Compared to two or three static NFB loop settings.
 

nickmm

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First, I would suggest that an educational video should show a person using a ’chopstick’ or some other non-conductive probe for the purpose he is using that screwdriver. I understand that this man knows tube circuits and that he has drained the caps, but that screwdriver just looks very much out of place when I see it probing into the circuit that way. So does a bare finger. I watched a fellow who is learning by reading and watching these videos, and I admit there is much to be learned in this type of video. However, I had to caution him about sticking his fingers down into a circuit and making contact with his finger as he was making some query or observational about his amp he had broguht by. one should never be lackadaisical about these dangers…especially during instruction. End of rant…..

As for the screen grid resistor vis-a-vis B+, that video doesn’t establish
any effect of that resistance and the screen grid current draw on the B+, does it?

The op seems familiar with the risks and procedures in working with high voltages.
I would not be commenting if I thought they were at risk.
I understand your rant.


It points out the the screen resistors are probably not responsible for the missing 40 or so volts.
I think you are correct pull the tubes bar the recififer and measure the voltages .
I think there is an issue with the filter caps in this amp as someone has been in there trying to correct problems.
Or the "fixes" have damaged the transformers.
 
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Wally

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The op seems familiar with the risks and procedures in working with high voltages.
I would not be commenting if I thought they were at risk.

My concern would be with novices…like the fellow who stuck his finger down into that circuit yesterday while holding the chassis in his other hand…..who are trying to learn on their own.
It is never advisable to get to the point that one is so relaxed about voltages that one uses a conductive probe…imho. Therefore, imho, it is not advisable to instruct through demonstration while using a method that could lead novices to grab just anything to,p probe around in a circuit. We all are going to get a shock doing this work, ime. Also ime one is more likely to get shocked when one is not being as attentive to basic safety as one should be. One of my basic safety rules is to never use a screwdriver or any other conductive material to probe a circuit.…at any time.
 

nickmm

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My concern would be with novices…like the fellow who stuck his finger down into that circuit yesterday while holding the chassis in his other hand…..who are trying to learn on their own.
It is never advisable to get to the point that one is so relaxed about voltages that one uses a conductive probe…imho. Therefore, imho, it is not advisable to instruct through demonstration while using a method that could lead novices to grab just anything to,p probe around in a circuit. We all are going to get a shock doing this work, ime. Also ime one is more likely to get shocked when one is not being as attentive to basic safety as one should be. One of my basic safety rules is to never use a screwdriver or any other conductive material to probe a circuit.…at any time.
I'm the son of an ex Naval electrical engineer.. Submarines. So even low voltages need care.
A Lot to be said of real world stuff not youtube and forums.
Are RCDs a thing in homes the states? They are a mandatory thing in Australia.
 

bluesholyman

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So not on every circuit?

Most, with some exceptions I suppose, require RCDs (GFCI) for devices that are within a certain proximity to water sources or anything outdoors and subject to rain. Otherwise, regular outlets with a circuit breaker in the panel is the norm here.
 

Wally

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New construction or reworking the electrical circuits in an older building requires GFCI outlets, iirc.
 

bluesholyman

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Post cap replacement - B+2 F&T cap is measuring 27uF on the meter. B+1 and B+3 are still 16uF for now - both around 17uF on meter.

So, with the JJ 5y3s in there, using the Eurotubes probe, I am getting 310v plate and 35mA current with the black glass Ruby's (120v measured at wall.)

With the Sovtek 5y3, no other changes, I am getting 350v plate and 40mA current, which puts it at 14w dissipation - thats pretty cooking I think. Not seeing any signs of red-plating from the Ruby's, but its black glass.....so....will have to look this evening when its dark.

I am beginning to think this transformer may not be the usual suspect for a 5e3 - its label says dbe-912 hb with a bunch of chinese characters below it, but I cannot find out any info about it. the sovtek seems to provide the juice, much more than the JJ.

I wonder if there were design decisions with regards to that power supply, the sovtek 5y3 and that 470 Ohm bias resistor - it would seem so.

My amp is apparently the Rev C version as shown from this image I got from RobRob's site:

937A3799-CEA6-4C28-84C1-B3A909658994.jpeg
 

nickmm

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With the Sovtek 5y3, no other changes, I am getting 350v plate and 40mA current, which puts it at 14w dissipation - thats pretty cooking I think. Not seeing any signs of red-plating from the Ruby's, but its black glass.....so....will have to look this evening when its dark.
That looks right.
Bump up the 250 ohm to 330 ohm if you want it to run a little cooler.
Call it a day, seems sorted as long as it is sounding good.
 




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