I finally got my TSE wired for testing and started going through the check out process,.. Using a Hammond 274BX (750ct) Without the 5AR4, I got ~-300V on the B-, 4.8V (Rectifier), 5V (300B), but 8.3V on the 5842 heaters,.. Is it normal for the unregulated 5842 heaters to be so high without a load on the amp? seemed like a lot.
I went back and plugged in the 5AR4, got ~530V B+, but now my B- is gone,.. pulled the 5AR4, retried to measure the B- and still nothing,.. I am assuming the DSEI12's are fried, though not sure why after one turn on.. I tried testing them (still in the circuit) and they test fine but something isn't happening,.. (also tried taking V reading from R5, still nothing),..
Am I missing something here? Thanks for the help!
I went back and plugged in the 5AR4, got ~530V B+, but now my B- is gone,.. pulled the 5AR4, retried to measure the B- and still nothing,.. I am assuming the DSEI12's are fried, though not sure why after one turn on.. I tried testing them (still in the circuit) and they test fine but something isn't happening,.. (also tried taking V reading from R5, still nothing),..
Am I missing something here? Thanks for the help!
I found some replacement DSEI12's, they are IXYS DSEP12-12A and are avalanche rated,... pretty much same spec's otherwise (from what I could tell) and are readily available at Digikey,... datasheet = http://ixapps.ixys.com/DataSheet/DSEP12-12A.pdf,..
Still curious about the Heater V on the 5842,... at ~+8V I'm afraid to stick the tube in as it is well above the published max V for the tube,.. Any thoughts? Thanks!
Still curious about the Heater V on the 5842,... at ~+8V I'm afraid to stick the tube in as it is well above the published max V for the tube,.. Any thoughts? Thanks!
None of the tubes are plugged in?
8 volts DC sounds about right. The capacitors charge to their maximum value, and if there is no current draw to pull them back down, then they sit at the fully charged voltage.
Put the power tubes in, which are protected by their regulator, ( BUT LEAVE THE RECTIFIER TUBE OUT SINCE YOU HAVE NO BIAS VOLTAGE ) and measure the voltage again at the 5842 sockets. I don't have a schematic handy, but best as I recall, there are not separate capacitors for filtering the filament voltage to the 5842's - just a resistor to set the final value. If they do have a separate filter capacitor, then the tubes would have to load that to measure the filament voltage accurately.
Hope this helps.
Win W5JAG
8 volts DC sounds about right. The capacitors charge to their maximum value, and if there is no current draw to pull them back down, then they sit at the fully charged voltage.
Put the power tubes in, which are protected by their regulator, ( BUT LEAVE THE RECTIFIER TUBE OUT SINCE YOU HAVE NO BIAS VOLTAGE ) and measure the voltage again at the 5842 sockets. I don't have a schematic handy, but best as I recall, there are not separate capacitors for filtering the filament voltage to the 5842's - just a resistor to set the final value. If they do have a separate filter capacitor, then the tubes would have to load that to measure the filament voltage accurately.
Hope this helps.
Win W5JAG
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Thanks Win, it does,... and makes sense.. Correct, no tubes plugged in,.. The only cap in the 5842 circuit is a 15000u that sits right before the 5V reg. I'll have to wait on the replacement diodes for the B- before I can put the 300B's in, otherwise I'm assuming they will 'runaway/redplate',...
On the B-, the first 'R' after the diode was specified as 270ohm. Playing around in PSUDII, I changed this to a 1.2K to help take the load off of the first cap after it, giving me ~440V... Using a 274BX that 1st B- cap was seeing ~550V (270ohm) and was only rated at 450V,.. You don't think that changing that one resistor would've had anything to do with the demise of the Diodes (DSEI12) do you?
Thanks for the insight!
On the B-, the first 'R' after the diode was specified as 270ohm. Playing around in PSUDII, I changed this to a 1.2K to help take the load off of the first cap after it, giving me ~440V... Using a 274BX that 1st B- cap was seeing ~550V (270ohm) and was only rated at 450V,.. You don't think that changing that one resistor would've had anything to do with the demise of the Diodes (DSEI12) do you?
Thanks for the insight!
The 300B's would probably run away if high voltage was applied without bias voltage to control them. If the 5AR4 is left out, then there is no positive high voltage to the power tubes or the MOSFET's, and no chance of run away. Without high voltage or bias, you are testing the filament circuit ....
I think George could better answer your second question. Capacitors can withstand a surge voltage for a bit above their normal working voltage, so a 450 volt cap should be OK at that position.
The problem with diddling around with the negative power supply is that it also constitutes the negative rail for the power mosfet follower, so fooling around here may have adverse unintended consequence. Hence, this is probably a question for George (TubeLab), who designed it.
Win W5JAG
I think George could better answer your second question. Capacitors can withstand a surge voltage for a bit above their normal working voltage, so a 450 volt cap should be OK at that position.
The problem with diddling around with the negative power supply is that it also constitutes the negative rail for the power mosfet follower, so fooling around here may have adverse unintended consequence. Hence, this is probably a question for George (TubeLab), who designed it.
Win W5JAG
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gotcha,.. didn't even think about 'No 5AR4, No B+' duh,.. lol, I will test that then,... yes, as far as the B-, I just seemed that I was seeing such a high B- with the 274BX that pulling it down a little would be good,... I also didn't have the specified 36k R's that connect to the FET source, had to use 33k,.. so was trying to shoot for the B- around ~250V, but in thinking about it, it is probably more about the relationship to the B+ on the FET drain,.. Not sure how to calculate the ma. draw on the FET to double check,.. study time I guess,.. lol Thanks again!
Possibly. I don't know. A lot of people do seem to fret about that, and have tried "modding" the negative supply, varying from using just one of the rectifiers, to changing R values. For almost everybody, it seems to work just fine as designed.
When I ran my TSE at high voltage, I used a lower voltage secondary to energize the negative supply. I figured this was preferable to putting increased resistance in the line, because of the MOSFET rail, but, if you want to modify the design, that is really a question for the designer.
Win W5JAG
Just to confirm the heater V,.. with tubes in it DOES drop to ~5.4V.. a touch on the low side but certainly better than being high,..
I did retry testing the B-,.. still nothing at R5 or R7,.. I did however check V across each Diode and got the expected ~350V,.. I guess this is because I'm really just reading the input V since the backside has a path to ground, so not really telling me anything as to the viability of the Diode,..
I did retry testing the B-,.. still nothing at R5 or R7,.. I did however check V across each Diode and got the expected ~350V,.. I guess this is because I'm really just reading the input V since the backside has a path to ground, so not really telling me anything as to the viability of the Diode,..
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