regulated DC heater supply

[bibster]

[Bbetter, to think it a highly questionable exercise to go DC. Having said that I have just been on a thread where a poor first time diyer has spend week tracking down a circuit hum, which turned out to be from the heaters.[/B]

That's me....
I'd say: If you have the possibility (by means of a scope) to track down the hum (IF ANY!!!), why bother DC-ing the heaters? (The audible diff. seems/appears highly subjective, the financial aspect if highly in favour of AC...)
If you find your amp hums, for no apparent reason, I'd say, like I found out the hard way, (I should' ve listened to Shoog before..) then compare the grid to the cathode+plate (wherever you take the signal of the tube). If there's a big discrepancy between them, shaped in a nice'n'lovely sine at you local powerline frequency, well... then it's yer heaters! (DC them than, if you have some margin (like 3 or more Volts) between your rectified AC and needed DC, then use some regulator; otherwise, like I did, just 'normal' filtering and (if needed) V-dropping)

JM2C,

Paul

 

[lndm]

I have used DC on indirectly heated signal triodes, and it didn't make things any worse. There is a caution, chip based Vreg's can oscillate. Gluca is advocating filtering after the reg, and this is the way to go, but some out there have neglected this, and had poor results.

If you reference the negative side of the dc supply to say 5 or 10 volts above cathode voltage then this guarantees only the cathode will emit electrons and not also the heater filament.

I would go a few volts more to allow for a greater cathode swing.

 

[jarthel]

I would appreciate it very much if the discussion on "AC vs DC heater supply" is done on another thread

This thread is about regulated DC supply

Thank you

ps. I would like to get back to the original topic and it's easy enough to create another thread.

 

[Gluca]

As said ... DC heating on IH tubes can be a questionable choice if there is no hum (coming from heaters). I just do it because my power tranny didnt have a 6.3V tap. Now I have the PCBs and I keep using them even now with a new tranny with the standard 6.3V. Did I notice any difference vs AC heating? No, I didnt so far. But that really depends on applications and tubes probably.

And yes, please duly filter the V feeding the LM. CLC would do fine or if you need to drop a few volt go for CRC. Small Ls are cheap. On a large 5A heater for my 813, I am using a large hammond choke in the filter feeding the LM. It wouldnt work without.


Your Q: are you saying that the 2nd 6922's heater pins are not connected?
I am saying the 2nd tube (I guess it is the other channel's tube) does need to be connected to the LM circuit only as it will be reference to ground/cathode (or where you elect to) thorugh the first tube's heater (that has got the 2 100ohm resistors etc...)

Hope it helps.

Gianluca

 

[jarthel]

Your Q: are you saying that the 2nd 6922's heater pins are not connected?
I am saying the 2nd tube (I guess it is the other channel's tube) does need to be connected to the LM circuit only as it will be reference to ground/cathode (or where you elect to) thorugh the first tube's heater (that has got the 2 100ohm resistors etc...)

Hope it helps.

Gianluca

please check if these steps are correct: (there are 4 tubes per channel. as an example the input section uses 2 6922 and the output section uses 2 8FQ7)

1. connect 2 100ohm resistor connected to pins 4 and 5 of the 1st 6922

2. tie these 2 resistors together and connect to the cathode of the 1st 6922

3. connect Vout of the LM circuit to pin4 and ground of the LM circuit to pin5

4. this is the hard part since I can't understand when you said "does need to be connected to the LM circuit only as it will be reference to ground/cathode (or where you elect to) thorugh the first tube's heater". I'm having some difficulty in understanding when you said "reference".

But i'll take a shot

pins 4 of the 2nd 6922 connects to pin4 of the 1st 6922 and pin5 of the 2nd goes to pin5 of the first?

 

[Gluca]

Jarthel I belive you are missing an important point or maybe I am not getting your Qs properly.

Yes there are two tubes in the input section but they are in the same envelope. 6922 is a double triode and it does have just one heater! And it does have two cathodes!

That said, the first 6922 should be in the left channel and the 2nd 6922 in the right one. Is this the case? If yes ...

1) OK
2) connect it the to higher voltage cathode
3) first tube's pins
4) the two tubes heaters (left and right channel) are in parallel so they are at the same voltage wrt ground and just one of them needs a connection via the resistors to the cathode (or ground or whatever point)
5) OK

You can find more references and examples on the (very useful and well written) book by M. Jones. He writes quite extensively about heaters (including LM dc heaters) with plenty of schematics. Unfortunately I cannot draw anything at the moment.

My suggestion is ... if you didn't build the amp ... just build it with AC heaters and add DC heaters later on.

Ciao
Gianluca

 

[jarthel]

I asked "tie these 2 resistors together and connect to the cathode of the 1st 6922"

you answered
2) connect it the to higher voltage cathode

based on the schematics (6CG7 are the 6922 in my example and 6H30 are the 8FQ7), the higher voltage cathode are those in the upper section?

I asked "connect Vout of the LM circuit to pin4 and ground of the LM circuit to pin5"

You said
3) first tube's pins

This part is what i do not understand. you said 1st 6922 only. What about the other 6922? Where do I connect pins 4 and 5 of the 2nd 6922?

4) the two tubes heaters (left and right channel) are in parallel so they are at the same voltage wrt ground and just one of them needs a connection via the resistors to the cathode (or ground or whatever point)

Somehow I think you meant to connect the 2 6922 heaters in parallel. So I'm thinking that pins 4 and 5 of the 2nd 6922 is also connected to the output of the LM circuit.

Thank you for your patience.

 

[Gluca]

Yes parallelled heaters. You can connect the 2nd tube's heater pins to the LM circuit outputs or to the 1st tube's heater pins (that should be easier).

Higher voltages are on the upper triode.

Take care, I understand from your Qs this may be your first attempt to build a valve amp ... high voltages can kill. If you are really a beginner pick up a simpler project ... Aikido is not that easy.

No problem. Happy to help.

Ciao
Gianluca

 

[arnoldc]

jarthel, you have to realize that in an Aikido circuit, the upper tubes' heaters must be referenced to a higher voltage. I actually posted my method on wiring them in the Aikido thread.

 

[jarthel]

jarthel, you have to realize that in an Aikido circuit, the upper tubes' heaters must be referenced to a higher voltage. I actually posted my method on wiring them in the Aikido thread.

could you tell me what particular page did you post your method?

I found a thread called "making sense of aikido calculations but it's 15 pages long.

thank you

 

[jarthel]

Yes parallelled heaters. You can connect the 2nd tube's heater pins to the LM circuit outputs or to the 1st tube's heater pins (that should be easier).

Higher voltages are on the upper triode.

Take care, I understand from your Qs this may be your first attempt to build a valve amp ... high voltages can kill. If you are really a beginner pick up a simpler project ... Aikido is not that easy.

No problem. Happy to help.

Ciao
Gianluca

I've buit a morgan jones headphone amp (with mods my Alex Cavalli) in the past but I am DIY audio is not really my expertise.

Have experimented with electrical/electronic circuits in the university so high voltage is nothing new to me.
====================
last question and it relates to transformer amperage rating.

say I need to heat up 2 6922 and let's say that the heater requirement is 6V@500mA for each tube.

Does that mean that the transformer must be able to output at least 1A or more?

or do I need to look at the wattage?

6V@500mA = 3VA per tube. so it'll be 6VA for both tubes.

I would then need a transformer than can reliably supply an LM317 (taking note of the dropout voltage) with the necessary voltag. And the transformer's VA rating must be be at least 6VA or more.

e.g. transformer has 12V rating and amperage of 500mA.

Thank you very much for the help and patience.