B+ on a superlite tmb

[mehfuzhoss]

Hello forum,
I am using resistors to decrease the B+ to 290 ish. I have already used the 'zener voltage dropping' method discussed on this site. But 4 zener diodes in series on the filter capacitor did not bring it down. So I used three 50 ohms resistors in series( 75 ohms 25 watt) soldered into B+ before it hit the rectifying diodes.

I turned on the amp and played for 10/15 secs, then powered off. On second power up, the amp has no sound. Is it possible that I might have fried the OT.

any suggestion and help is appreciated.

Thank you.

[Bieworm]

First.. what’s the B+ you start with before dropping it? I mean, how much do you intend to drop?
Second.. I find it very weird that the zeners don’t drop any voltage. Did you orientate them correctly?
Third.. resistors are not that great nor efficient to drop voltage at that position. I suggest to use an appropriate power transformer with the right voltage to start with.
No sound can mean a lot. But a fried OT is very unlikely. Can you post pics if the amp? Also, a voltage chart with the actual voltages would be very helpful

files/JMPGuitars_18_Watt_Superlite_TMB_ ... _Chart.pdf

[mehfuzhoss]

thanks for the voltage chart. will post back soon.

[mehfuzhoss]

Correction:
"I turned on the amp and played for 10/15 secs, then powered off. On second power up, the amp has no sound. Is it possible that I might have fried the OT, because one end of B+ was not soldered. I soldered it back on. But still no sound, and very low voltage on filter capacitor.

any suggestion and help is appreciated.

[Bieworm]

If low voltage on filter cap you might wanna look at the rectifier or even the power transformer.
What’s the voltage measured across the HV winding?
Are you using a SS or a tube rectifier?
Pics of the guts would be helpful.

[mehfuzhoss]

I got the amp up and running. My AC main: 122.7; B+ 311AC; 218DC & 206DC on Filter cap (used 5 zener diodes 30v, 5watt ) OT plate voltage on power tubes 212V.

preamp V1: pin1: 105; pin3: .75, pin6: 83.2
Preamp V2: pin1: 142; pin3: 28.6, pin6: 41.1

EL84: pin7: 212DC on both

the amp sounds clean and i get fair amount of overdrive with gain at max and vol at 2. I am happy how it sounds with this voltage setting.. I would like to hear from experts if these voltages are within safe limit.

Thank you.

[JMPGuitars]

That doesn't make sense. I'm assuming when you say B+ you actually mean the PT secondaries (311-0-311). B+ is the DC rectified voltage coming from your rectifier tube or diodes. Target B+ is 345VDC.

For voltage reference and comparison, look at the voltage documents in the downloads section.

Thanks,
Josh

[Bieworm]

That doesn't make sense. I'm assuming when you say B+ you actually mean the PT secondaries (311-0-311). B+ is the DC rectified voltage coming from your rectifier tube or diodes. Target B+ is 345VDC.

For voltage reference and comparison, look at the voltage documents in the downloads section.

When you do the math based on his voltages he’s using a 225-0-225VAC or 0-225VAC secondary. But I’m afraid that will remain a mystery. OP doesn’t do the answering questions thingy

[JMPGuitars]

When you do the math based on his voltages he’s using a 225-0-225VAC or 0-225VAC secondary. But I’m afraid that will remain a mystery. OP doesn’t do the answering questions thingy

He said five 30V 5W Zener diodes to drop B+??

[Bieworm]

When you do the math based on his voltages he’s using a 225-0-225VAC or 0-225VAC secondary. But I’m afraid that will remain a mystery. OP doesn’t do the answering questions thingy

He said five 30V 5W Zener diodes to drop B+??

Right! In that case I still think he’d better use a suitable transformer. There is an awful lot of waste/heat thrown away
For my 6AQ5 amps I use a 250-0 VAC HT secondary transformer, and I still need to zener the B+ down like 25V

[JMPGuitars]

He said five 30V 5W Zener diodes to drop B+??

Right! In that case I still think he’d better use a suitable transformer. There is an awful lot of waste/heat thrown away
For my 6AQ5 amps I use a 250-0 VAC HT secondary transformer, and I still need to zener the B+ down like 25V

Yes, but we don't know what he's using. Even if the Zeners are poorly placed at ~50% efficiency, he's dropping around 75V. If they're after the first filter cap, that's 150VDC! Why?? Get the right PT, or set the right targets.