New build startup issues

[Ron Worley]

I've run into some kind of stumbling block fellas.... Hep me!

Powered Teri Lin up with the bulb limiter and no tubes. All seemed OK- resonable plate voltages, 6.4 on the heaters... One weird thing was that the B+ (no tubes) was almost the same on all B+ (1-5). V846 emailed me that this was normal with no load (tubes) in the circuit.

Threw in the tubes, fired it up (no standby) - short flash on the bulb limiter (caps charging I think), settled down to a very dull glow. Looked at the tubes- no heater glow and almost zero on the heater V.

Powered down, drained caps, pulled tubes, then fired up again... Heater V is normal... WTF???

V846 mentioned that it could be a bad ground on the heater center tap or a bad PT.... I will check the tap ground solder connection tomorrow.

Any thoughts on what could be wrong and a way to test the tranny????

Thanks in advance,

Ron

[Richie]

After you try some of the other suggestions,

it could be a bad tube, read the volatge from the first part of the string..if its there, then read it through the sections..is it all tubes with no heater voltage? Check the solder connection on heaters on the first tube hookup.
also look close for any small bits of stray wire or clippins that might be causing a problem

[Ron Worley]

Richie-

I checked the voltage at V1 pins 4&9 without tubes- it's at the end of the heater harness, so that tells me it's wired right.

I cleaned the chassis out with a can of compressed air making sure that any source of shorting was removed.

When installed, none of the tubes heat up, and voltage at V1 again are almost zero. The tubes are brand new and were tested by KCA. The PI is even a matched tube for even push-pull operation.

My electrical circuit knowledge is OK, but not great when it comes to tubes and trannys... so I'm stumped.

[Bob-I]

Did you test with one tube at a time? If not, that'd be my next step, it's possible for a tube to go bad and you'll find it by testing one at a time. Is the heater centertapped or are you using 2 100R resistors as a false centertap?

It's normal for all B+ voltages to be the same with no load. V=IR with no I there's no drop across the R.

[Richie]

Richie-

I checked the voltage at V1 pins 4&9 without tubes- it's at the end of the heater harness, so that tells me it's wired right.

I cleaned the chassis out with a can of compressed air making sure that any source of shorting was removed.

When installed, none of the tubes heat up, and voltage at V1 again are almost zero. The tubes are brand new and were tested by KCA. The PI is even a matched tube for even push-pull operation.

My electrical circuit knowledge is OK, but not great when it comes to tubes and trannys... so I'm stumped.

Even new tubes, tested by whoever can be duds when you get them. It happens. As Bob posted, try one tube at a time.. Are they lit,or can you see the heater glow in any of the tubes? How are you measureing the heaters..? got any pics? Also make sure the sockets are wired correct.. if you have voltage with tubes out..and none when the tubes are installed.. you could have one of the pins wired wrong.

[Ron Worley]

This weekend I will do a real thorough scrub of the pinout, cold joints, an do one tube at a time...

It's got a center tap, will check that joint too.

Richie- the pics are posted in my other post- "First Build, don't laugh too hard"..... I ain't laughing now!!

Thanks for everyone's help so far!!

Ron

[Bob-I]

This weekend I will do a real thorough scrub of the pinout, cold joints, an do one tube at a time...

It's got a center tap, will check that joint too.

I once mixed up the CT with an AC lead. Took days to figure out the heaters.

[Ron Worley]

Driving home last night, I got a flashing battery light in the Bimmer.... took it in this morning...$700 for a new alternator...

The good news is that I couln't make it to work today, so I got to piddle with the amp some mo....

Took advice from V846 and cleaned out all tube sockets, checked pinout on sockets, checked for any contacting socket lugs, etc. I did not find anything, but may have moved it along to somewhat more success...

Installed tubes one at a time, measuring heater V each time and adding the next tube with the previous installed:

V1- 6.4V
V1+V2- 6.3V
V1-3- 6.19V
V1-4- 5.745V
V1-5- 5.568V This seems low to me- is it???

That looked OK enough to me to attempt some B+.... Threw the standby- no major glow on the limiter.... So I measured B+:

B+1- 262.4
B+2- 257.9
B+3- 215.8
B+4- 205.6
B+5- 196.7

Obviously this not right....but the bias was at max negative.

So I checked the bias V-it's range was only -18 to -26

So something is really not right here at all...

Any further ideas???

Ron

[dartanion]

Did you cook your diodes or possibly hook them up backwards?

[Ron Worley]

Nope, checked them out with Mr. Fluke meter's handy diode checker.. they're just fine...

Ron

[Firestorm]

Ron--

Which PT are you using? There's no way the heaters should drop that much if the PT is up to the task.

The low bias voltage is troubling, too. Your power supply board looks right, though I can't make out how your bias pot is wired. The revised Kelly schematic shows wiper and one end grounded (safest way since it fails to a higher bias); Francesca looks to have the bias connected to the wiper itself -- would work fine, but not as safe.

And then the B+ voltages are just not right. Since your bias is off, you could be dropping a lot of voltage through the power supply. Try to get the bias to -33VDC (check the bias pot -- 25K?, maybe increase the 47K resistor) and see what the B+ looks like then.

[fishy]

Ron,
Looks like the V2 - V3 filament wiring is not right looking at the photos on the other thread. Check pin9 goes to 9 and 4/5 go to 4/5...
It looks to me as if pins 4/5 on V3 go to 9 on V2

[Ron Worley]

It's a Toneslut PT using the 6.6K taps.

The heaters are wired correctly Pins 9-9-9-7-7 and 4-4-4-2-2 (4 is jumpered to 5 on preamps tubes). Checked them with the DMM...

The bias pot is wired so that one side is connected to the bias resistor, the wiper is connected to the caps (and ground), and the other side is connected to ground (using a jumper under the board). The pot is a 25K (but it read only 18K with the DMM). The bias resistor is a 56K per a suggestion from Allyn Meyers.

Yeah, it all does not add up... is my PT the issue itself?? It just seems weird to have low B+ and have the heater V drop successively as tubes are introduced ( in standby of course).

[geetarpicker]

Ron,
Looks like the V2 - V3 filament wiring is not right looking at the photos on the other thread. Check pin9 goes to 9 and 4/5 go to 4/5...
It looks to me as if pins 4/5 on V3 go to 9 on V2

Correct, it looks like the polarity is reversed at V2. However in an original (at least in mine and Francesca...) the polarity IS swapped on V1. However Ron's got it reversed at V2. Should work though either way, but it might hum more the way Ron has it. Seems like KF had a plan there.

Still, I'd first really check the tube wiring overall. Also be sure the output tube sockets were oriented the correct way in regards to the alignment pin. This would make a world of difference.

All that said, have you tried some other tubes? Try swapping all of them.
I suspect a partial short in your filaments, either wiring or a tube. Something is bringing ALL the voltages down. The B+ in an original Wreck is over 400v, around 415-420v in mine and my two clones even when biased at 45ma.

[Firestorm]

It's a Toneslut PT using the 6.6K taps.

The 6K6 taps are on the OT. What kind of PT is it? Toneslut?