TSE 300B Initial checkout problems. Help please.

[Mark Fugate]

I am building a TSE with 300B tubes and the initial checkout is not going well.

My B+ 457 Volts, 5842 plate voltage is also 457 Volts, and R5 (270 Ohm 2W) glows red.

My power transformer is an Edcor XPWR131-120 with the following wiring

W 330 V CT T1-1
Y

​

2.5 V T1-2
Y 2.5 V T1-3
R 330 V T1-4
O 330 V T1-5
BR 3.15 V T1-6
WBR 3.15 V CT T1-7
BR 3.15 V T1-8
​

Thanks much in advance for any and all assistance.

 

[JonSnell Electronic]

R5 is your negative bias supply and only feeds C6 and R6. Check C6 is the correct way around.

 

[Mark Fugate]

C6 and C7 are correctly oriented,

Any other thoughts?

 

[JonSnell Electronic]

To make R5 heat up there is obviously a heavy load. The resistor following is 10k so it is either a solder bridge on C6 end, or it is magic. Nothing else can cause that.

 

[Mark Fugate]

Maybe a bad C6?

I replaced the 270 ohm resistor, powered things up, and C6 started smoking.

 

[Mark Fugate]

Could a shorted C6 cause me to see full B+ (450+ Volts) on the 5842s?

Thanks much for your comments.

 

[JonSnell Electronic]

If C6 is short, you will have no negative bias and the output valve will complain by getting extremely hot very quickly.
Full HT on the anode of the 5842s is a bias issue on those valves. If they are not biased correctly, (turned off) full HT will be on the anodes.
Sort out your -ve bias voltage first. One step at a time.

 

[JonSnell Electronic]

Have you got -200volts roughly on C6?

 

[Mark Fugate]

-508 which seems impossible. I will recheck. Confirmed.

The voltage across R7 is 0

 

[JonSnell Electronic]

Check your wiring, C6 must have no more than about 220v ish, certainly not 508!

 

[JonSnell Electronic]

Looking at your chosen transformer, 330 0 330 will give you around 500volts so maybe a change of value for R5 to drop the voltage to a useable level.

 

[Mark Fugate]

What if I use 330 0 260?

I must add that I appreciate your patience and willingness to help.

 

[colnago55]

I think you wiring is wrong. I'm using the same transformer for my 300B.

On mine the two brown wires are in the 7 & 8 slots and the brown and white in the six slot.

Otherwise I believe we match up.

good luck.

 

[Mark Fugate]

Thanks guys!

 

[Mark Fugate]

Gentlemen,

I just changed my transformer secondary to 260-0-260 and I now have B+ = 414 Volts and B- = -195.

I also changed the filament wiring as suggested by calnago55.

I still do not think that I am out of the woods because all other forum posts I find for 300B TSE use the 330-0-330 windings.

 

[Mark Fugate]

I 'think', (KEYWORD 'Think') things may be working since making the transformer change.

It puzzles me that I can not find anyone else using the secondary windings that I am using.

Any thoughts, comments, and ideas are greatly appreciated.

 

[mkane77g]

voltage checks don't lie

 

[colnago55]

I am using the 330 taps on the same transformer and my B+ is around 360. My 5842's are set at 175.

I'm using a choke and a motor run capacitor.

What is your set up?

 

[Mark Fugate]

mkane77g - you are absolutely correct! I neglected to check my variac output and as you have guessed, the variac output was 141 volts.

Color a deep and very bright shade of 'stupid'.

Thanks again guys