1st build; Adding load to PT secondary

cancon · 16th October 2011, 05:51 AM

Dear reader:

The power section in my home-made design is overpowering the circuit I've built; single-ended, 1ea 6V6 & 12AU7, 5k-8w OT.

The PT secondary is rated at 250vac @ 42mA and 285vac @ 0mA (exhibiting a linear voltage change between 0-42mA).

In circuit I measure 275vac before the bridge rectifier and 375vdc after the filter section (150uf/350 & 20uf/350). My circuit isn't putting a dent in the load on this transformer and I need an operating voltage of 250vac.

Please advise!

aardvarkash10 · 16th October 2011, 06:04 AM

PSUDII

Its all there for you.

DF96 · 16th October 2011, 02:15 PM

How much current is the 6V6 taking?

cancon · 16th October 2011, 04:41 PM

I'll measure when I have a chance soon.
Right now the amp is not working very properly...there is arcing in the 6v6, strange oscillation noises, no signal at all - even when the effect is bypassed...(half-true bypass...input tip is shunted to output tip, but input tip is never actually disconnected from the screen of the 12AX7. Signal does bypass properly if the unit is off however), the input tip is actually hot as well, gave me a bit of a bite.

I'll try to get that measurement soon. thank you!
I'll check out that link too, looks promising Aardvark!

aardvarkash10 · 16th October 2011, 06:37 PM

you have a bigger problem than B+ voltage.

A schematic and measured voltages (tubes out) would be a good start.

cancon · 10:32 PM

Please please please excuse my amateur drawing skills. First schematic i've ever drawn, did this up with tinycad. Unless otherwise noted all cap values are uf/VDC & resistor values are ohm/1/4watt

Much appreciated!

Excuse the original PT 205 rating, that was what I was copying. In reality it was more like 225 because of the 115V tap and my 120-122V actual supply. My revised target (based on current stock and prices) was 250V, but there is also a 125V tap. I figured that if I hit 42mA I would achieve between 240-250 which would be ideal.

Can you tell me exactly which measurements you'd like?

aardvarkash10 · 16th October 2011, 10:43 PM

very odd front end - do you mind describing what is meant to be going on from the input jack to the second section of the ax7? Don't worry about voltages at this point.

aardvarkash10 · 16th October 2011, 10:47 PM

sorry - kinda got it now...

costis_n · 16th October 2011, 10:56 PM

100K in series with the power transformer primary?

cancon · 16th October 2011, 11:54 PM

All I can say...this is not my brainchild...I copied it from an existing design. I think it is very similar to a fender champ. This is meant to be a tube head "preamp"...feeding an unbalanced tube driven Leslie speaker (which does not have a built-in pre), hence the 10ohm/5w resistor across the OT.

I feel that there are 2 problems...but I can only pinpoint one - I'm supplying the circuit with too much juice. I want the transformer to deliver under 250v so I need a full load, possibly by adding beefy resistors before the bridge?

Anyhow....let me know if your diagnosis requires any present voltages.

16th October 2011, 05:51 AM	#1
cancon diyAudio Member Join Date: Mar 2011	1st build; Adding load to PT secondary Dear reader: The power section in my home-made design is overpowering the circuit I've built; single-ended, 1ea 6V6 & 12AU7, 5k-8w OT. The PT secondary is rated at 250vac @ 42mA and 285vac @ 0mA (exhibiting a linear voltage change between 0-42mA). In circuit I measure 275vac before the bridge rectifier and 375vdc after the filter section (150uf/350 & 20uf/350). My circuit isn't putting a dent in the load on this transformer and I need an operating voltage of 250vac. Please advise!

16th October 2011, 06:04 AM	#2
aardvarkash10 diyAudio Member Join Date: Mar 2007 Location: Auckland, NZ	PSUDII Its all there for you. __________________ "Folks, you can't prove truthiness with information. You prove truthiness with more truthiness. In a process known as truthinessiness." - Stephen Colbert, The Colbert Report

16th October 2011, 06:37 PM	#5
aardvarkash10 diyAudio Member Join Date: Mar 2007 Location: Auckland, NZ	you have a bigger problem than B+ voltage. A schematic and measured voltages (tubes out) would be a good start. __________________ "Folks, you can't prove truthiness with information. You prove truthiness with more truthiness. In a process known as truthinessiness." - Stephen Colbert, The Colbert Report

16th October 2011, 10:43 PM	#7
aardvarkash10 diyAudio Member Join Date: Mar 2007 Location: Auckland, NZ	very odd front end - do you mind describing what is meant to be going on from the input jack to the second section of the ax7? Don't worry about voltages at this point. __________________ "Folks, you can't prove truthiness with information. You prove truthiness with more truthiness. In a process known as truthinessiness." - Stephen Colbert, The Colbert Report

16th October 2011, 10:47 PM	#8
aardvarkash10 diyAudio Member Join Date: Mar 2007 Location: Auckland, NZ	sorry - kinda got it now... __________________ "Folks, you can't prove truthiness with information. You prove truthiness with more truthiness. In a process known as truthinessiness." - Stephen Colbert, The Colbert Report


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16th October 2011, 02:15 PM	#3
DF96 diyAudio Member Join Date: May 2007	How much current is the 6V6 taking?

16th October 2011, 04:41 PM	#4
cancon diyAudio Member Join Date: Mar 2011	I'll measure when I have a chance soon. Right now the amp is not working very properly...there is arcing in the 6v6, strange oscillation noises, no signal at all - even when the effect is bypassed...(half-true bypass...input tip is shunted to output tip, but input tip is never actually disconnected from the screen of the 12AX7. Signal does bypass properly if the unit is off however), the input tip is actually hot as well, gave me a bit of a bite. I'll try to get that measurement soon. thank you! I'll check out that link too, looks promising Aardvark!

16th October 2011, 10:56 PM	#9
costis_n diyAudio Member Join Date: Aug 2008	100K in series with the power transformer primary?

16th October 2011, 11:54 PM	#10
cancon diyAudio Member Join Date: Mar 2011	All I can say...this is not my brainchild...I copied it from an existing design. I think it is very similar to a fender champ. This is meant to be a tube head "preamp"...feeding an unbalanced tube driven Leslie speaker (which does not have a built-in pre), hence the 10ohm/5w resistor across the OT. I feel that there are 2 problems...but I can only pinpoint one - I'm supplying the circuit with too much juice. I want the transformer to deliver under 250v so I need a full load, possibly by adding beefy resistors before the bridge? Anyhow....let me know if your diagnosis requires any present voltages.

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