New build startup issues

[Firestorm]

A couple more questions: where is your PT center tap grounded? I can see green/yellow and red/yellow wires in the build. Were these surplus PT wires you clipped? If this is a Tone Slut PT, the red/yellow would have come from the center tap. Waste not, want not, I suppose, but it's a little confusing visually.

[Ron Worley]

I'll check the heater polarity again, but I just did it with a meter....it checks out....

It's a toneslut tranny, and I misspoke due to overthinking... I meant to say 300V taps...DOH!

Center tap is grounded, but there's no way to check that joint without pulling the PS board out and really screwing up some lead dress... I may have to... but is there a way to check this via the heater wires with power off??, i.e. measure the resistance across the tap and each heater wire???

Yes, this wires are surplus clippings.... I got the idea from the undocumented 90 Express- see the files section... KF did the exact same thing.. and for good reason I think. IMHO, using 20 AWG 300V solid core wire (like I think I see in Franny) isn't a good idea... I uprated all B+1-3 carrying wires to heavier stranded, 600V wires.

Keep the ideas coming, and thanks to all!

Ron

[Ron Worley]

OK, It DID check out with a meter, but I discovered that it WAS wrong between V2 and V3 by physically tracing it (which I should have done before).

BUT what is weird is that if I measure resistance across pin 4 and 9 of any preamp tube (or power tube on their heaters), I get a dead short- zero ohms.

My tranny theory sucks, so I don't know if this is normal when un-powered...

Could it be that the center tap isn't working?? Can I rig up an artificial tap using the 100ohm resisters on V5?????

[Firestorm]

There are two different center taps to be concerned with: the red/yellow wire is the center tap for the 300-0-300 taps (and the 260-0-260 taps which you aren't using). That ground has to be good or the transformer won't work right. There is also a a brown/white lead, which is the center tap for the heater winding. The heaters should work whether that's grounded or not (in which case you's use two 100R resistors or a hum balance pot to reference the heaters to ground).

You can measure resistance from either end of the winding to the other end and to the chassis ground to make sure everything is connected. (When you measure the heater winding, pull the tubes -- the low current of your DMM will make the heaters look like a dead short from side to side). And with the amp on you can measure the AC voltage from end to end and to ground to make sure you see the "right" numbers. Something is clearly kerflooey: heater voltages and B+ are just too low.

[Ron Worley]

I checked- yes, I have both center taps grounded, I even undid the lug (THAT was a pain in the ass to get back in!) and redid the solder joint.

I pulled the tubes, and I still have a dead short from pins 4 to 9

Measured R between both pins 4 and 9 (and at the actual heater wires at V5) and the center tap- I get a dead short there too... Shouldn't there be some level of resistance?? i.e. 100 ohms (presuming that base on the artificial tap resistor values)????

[gearhead]

Go upstream and start at the top. Power into amp as Volts AC (120-ish) and Volts AC out of the PT secondary measured before the diodes (nominally 600VAC).

What's the VDC at the juncture of the two 40 uF filter caps with the standby still off? In other words before the rest of the circuit kicks in and loads it down.

WRT the heater, no, you will not find a lot of resistance. Try doing a continuity check between the heaters and ground. Your buzzer/beeper will go off.

[Ron Worley]

Thanks for kicking in GH...

Put the tubes in, the secondaries read about 230V in standby, 205 on....

Me thinks that I have a bad tranny, either as delivered or by induced stupidity....

Ron

[gearhead]

Did you measure the voltage in? At the switch.

Especially: Measure between the diodes, not one or the other to ground for PT secondary voltage.

[skyboltone]

Cold filaments will show near 0 ohms. Rip out the plate spike diodes for now. If you feel you need them stick them in later. The filaments are wired right. I can't see the grid stop resistors.

[Ron Worley]

Pics are in a previous post- "First Build, Don't Laugh Too Hard" or something like that- it's not too many below this post at this point.

I have the pin numbers figured out, but it never hurts to ask...

Measured across the secondaries (didn't understand that point at first).

Got 460V in standby, 408 On... way low..

[skyboltone]

Pics are in a previous post- "First Build, Don't Laugh Too Hard" or something like that- it's not too many below this post at this point.

I have the pin numbers figured out, but it never hurts to ask...

Measured across the secondaries (didn't understand that point at first).

Got 460V in standby, 408 On... way low..

You were posting as I edited mine. Rip out the diodes. It looks like you only have one anyway. That might explane the lack of plate voltage but the filaments is a bit of a puzzle. 460 would be about right for the 260Vac taps unloaded. What do you get at pins 4/5 and 9 while in standby with pre tubes in? Leaving the Power tubes out for now.....as a matter of fact lift the high voltage leads to the PS diodes for now. Let's iron out these cold tubes first.

[skyboltone]

I checked- yes, I have both center taps grounded, I even undid the lug (THAT was a pain in the ass to get back in!) and redid the solder joint.

Both center taps?.....you mean the center tap for the HV tap and the center tap for the 6.3V taps? If you are using an artifical center tap for the filaments you don't land the CT from the 6.3V winding. You can't have it both ways. Just talking out loud here. If you mean you have both HV center taps grounded you've possibly grounded a bias tap. Heyboer uses a red/white stripy and a red/ 'nother color stripy for bias and HV center tap. Like I say, I don't know the toneslut tranny specifically.

[gearhead]

Toneslut Tranny:

[Ron Worley]

I have the brown with white stripe heater center tap and red with yellow Primary center tap grounded. No artificial tap installed.

I only have one diode?? I have two each side in series like it supposed to be..... I don't understand.

So I should undo the diodes to the secondaries, then what??

I recorded the heater voltages as I slowly added tubes- it reduced with each one (value posted on the 1st page of this post).

I do like the idea of isolating things to get at the possible source.

Because I've made similar mistakes, when you measure B+, it is in reference to the chassis ground??

[Ron Worley]

I have that pic of the trannys, and it's wired up like it says...

I checked the clipped leads all four (2 260V wires, and 2 5V wires) are securely shrink tubed..

I think that Skyboltone is onto a logical path...

I gotta quit for tonight, will have a go at it tomorrow night after work- plus, hopefully more folks will chime in with ideas / answers... I am sure out of them...
On the bright side, I am learning so much, it's a wonder I was smart enough to remember to breathe before!