Heater Supply Circuits-AC and DC

[CJ]

this is my favorite, low hum, no frills, always works,

resistors burn up if you get a short plate to heater,

"save the transformer" foundation, join today!

 

[CJ]

getting back to basics>

 

[CJ]

and finally the primitivo circuit,

can be made quiet if you are a 90 year old tech from the old school,

 

[johnheath]

Great topic with a lot of answers for a lot of people …Thanks

/John

 

[mattamatta]

memory capacitors?  ???  maybe scrounged out of disposable cameras? 

Caps out of a disposable camera would probably be smaller value very high voltage for the flash generation.  I would probably have labeled those "supercaps" on the schematic and that's a good search term to keep in mind for anyone attempting to find something like a 47,000uf 5V cap.

 

[CJ]

that schemo with  the memory caps was from Eric Barbour, maybe i will shoot him an email to see what he means,

could be computer caps, those big blue Sprague things that can be had for cheap,

 

[PRR]

> Fisher 500C has some weirdness (translate-do not understand) 
> has a -22 V-dc series string on a few 12AX7's,
> and some funny caps on the upper string

The 22V (two under-heated 12.6V heaters series) is probably also a bias supply for the finals, which is why it is negative. (Rectifiers were too costly to throw-in another if one could do two jobs.)

The funny caps are probably the tubes in the IF string. There's a gain of maybe a million from IF in to IF out. Then you have wires running from one end to the other, eager to carry IF Out signal back to the In. So caps everywhere, and some smutz which may be inductors (beads)?

"Memory Caps" are "Super Caps", activated carbon electrolytic, used for low-low-tiny current drain to keep CMOS memory alive when power is off. Traditionally they have huge ESR, make poor 60Hz filter-caps. Recent ones are far better.

 

[CJ]

another bone for the stew pot,

Peavey Roadmaster heater supply has a 25 volt DC bias on the tubes,

 

[mjrippe]

How does the cap lower the required wattage rating of the pot?  Isn't it there to block the +25v DC?  Also, shouldn't they be using 35v caps ;-)

 

[CJ]

good catch! yes the cap blocks the DC , posted too late in the evening, 

still gonna have 6.3 V-ac across the pot, so wattage does not change,

that cap might pop in a plate to heater short unless all those fuses work first,

bias supply could take a hit also,

 

[CJ]

another heater circuit that uses 47 ohm 1/2 watt resistors to create a virtual center tap,

normal value here is 100 ohms each, so this is a little stiffer of a CT,

dissipation is 6.5/47*2=69.15 ma * 6.5=0.45 watts/2=0.225 watts in each of the 47 ohm resistors or about 1/4 watt out of a 1/2 watt which is ok, possibly, we would probably go with 1 resistors over here,

 

[CJ]

HP 400D AC voltmeter from the 50's has DC heaters,

this is because it has a 1 mv input range

clever series resistor scheme,

adjustable also>

 

[ruffrecords]

Cool stuff CJ. Where can I buy 58,000uF capacitors!! I like the idea of using a single beefy diode on the dc side to drop a fixed voltage - neat.

Cheers

Ian

 

[PRR]

> Where can I buy 58,000uF capacitors!!

http://capacitor.tedss.com/58000uF

I have no idea who that is, just came up first in Google.

Appears to have once been a Standard Value, because old NOS show up in many places.

 

[ruffrecords]

> Where can I buy 58,000uF capacitors!!

http://capacitor.tedss.com/58000uF

I have no idea who that is, just came up first in Google.

Appears to have once been a Standard Value, because old NOS show up in many places.

Odd indeed. 68000 I could understand but 58000 is a new one on me. I wonder where that value came from - I notice a few of the caps are 75V rated and appear to be 'telecoms' related - old telephony types? They all seem to be in the US. Google UK gives some on UK ebay but they are all from the US.

Cheers

Ian

 

[PRR]

Totally strange....

I again Googled "58,000uFd capacitor" and this time one of the links is to THIS thread.

"Thursday, November 20, 2014
Lee Marvin & Pussy"

http://twogoodears.blogspot.com/2014/11/lee-marvin-pussy.html

Top link in left column "TGE's Picks - My Blogs and Sites List" is (at the moment) this thread.
_____________________

The few non-audiophile links for {that size cap} mention "ringer", so it may be a Ma Bell compatible ringtone generator part.

 

[CJ]

well,  he has a big organ but does he know which knobs to pull?

 

[saint gillis]

Awesome information collection CJ!

A friend of mine told me that DC in the heaters could after a long period of time polarize the heaters which was not good, and he said it was good to have a switch to reverse the 2 heaters supply pins time to time , to avoid heaters polarization, what do you  think of that?

 

[ruffrecords]

Awesome information collection CJ!

A friend of mine told me that DC in the heaters could after a long period of time polarize the heaters which was not good, and he said it was good to have a switch to reverse the 2 heaters supply pins time to time , to avoid heaters polarization, what do you  think of that?

I think it is rubbish. LOL

There is a whole group of tubes designed for battery radios that had dc heaters. They never had any problems and the heaters were not made any different.

Cheers

Ian

 

[Andy Peters]

A friend of mine told me that DC in the heaters could after a long period of time polarize the heaters which was not good, and he said it was good to have a switch to reverse the 2 heaters supply pins time to time , to avoid heaters polarization, what do you  think of that?

"Polarize the heaters?" I'd love to hear the explanation of that phenomenon.