new build is now happy

[talbany]

Darin
With the tubes out and limiter in check to make sure your neg bias voltage on the grids (pin 5) is stable w/decent range
BTW..W/limiter in is the amp getting the proper line voltage?...Your voltages look low..

Tony

[dcribbs1412]

Tony
I don't think its working
voltage on pin 5 is not stable
120V at wall
power tubes out
re post of voltages B+ 3..455V B+4..335V B+5..327
V1..198,205 V2..206,219 V3 312,304
these readings look closer

[talbany]

Now pull the limiter and no tubes.. Is it still unstable?..

Tony

[dcribbs1412]

Tony last voltages where no limiter...
I have 3.3v on both filaments
I am measuring the wiper of the bias pot DC to ground right? for neg voltage

Now pull the limiter and no tubes.. Is it still unstable?

[talbany]

I am measuring the wiper of the bias pot DC to ground right? for neg voltage

Yep!!...You should have a stable range around -20 to -60 for a pair of 6L's.. Go over your bias supply again make sure all your grounds are tight.. You can also disconnect your bias supply feeding the pot and make sure that's a stable point first..If it is you know it's either the pot or the grid feeders..Also check to make sure nothing is touching pin 5 on each tube and everything is wired correctly.. Probably something simple..

Good Luck

Tony

[talbany]

Darin
Looking over your bias supply.. Why do you have a 2 wires attached to the wiper (purple and white).. If the white is the supply coming off the board it should go to the bottom of the pot (not the wiper) and the purple to the 220K grid feeders or am I seeing things.. If your white wire is the bias feed your tubes will stay in cutoff..

Tony

[dcribbs1412]

Tony
I going by the 183 bias layout
which has bias 1 (yellow) and 2 (white) from the board and the purple
to the 220ks

is that right or am I not seeing things right


Darin

[M Fowler]

https://tubeamparchive.com/viewtopic.php?t=13095

Version 11 is in above thread.

[talbany]

Darin
Ahhh OK.. I have never set up my bias supply like 183 so I can't tell you what's going on there.. I did notice though that your bias caps look backwards (as opposed to the 183 layout) or am I not seeing this right..

Tony

[dcribbs1412]

Could be Tony I assumed the black lines where neg side

[dcribbs1412]

https://tubeamparchive.com/viewtopic.php?t=13095

Version 11 is in above thread.

Thanks Mark
that's the one I am referencing

[talbany]

Cool OK..The black lines looked like the dimples..Also one other thing I see is it looks to me like the ground plane that runs along the bottom of the board where you have ground wire looks to be on the same plane as the white wire that feeds the wiper..Is that bias board PCB the same as what's in the 183 layout or am I missing something..

Tony

[heisthl]

Tony
just so I'm sure what your asking
I have the meter on DC black lead in black bias jack
and red in red jack...I get 0 mv when I sweep the bias pot no tubes in
I hope this is right...

That's normal - there could be no current flow through the 1 ohm with no tubes in. Is there negative voltage on the wiper of the bias pot?, on the grid resistors of the output tubes?

[dcribbs1412]

Is that bias board PCB the same as what's in the 183 layout

I'm pretty sure it is

heisthl wrote

Is there negative voltage on the wiper of the bias pot?, on the grid resistors of the output tubes?

no sir no voltage

Darin

[talbany]

That's really strange I can clearly see 2 etches that run to that white wire and your board posted only shows 1.. Anyone else see this or is it just me..

Tony