7806 heater issue

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didit
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Re: 7806 heater issue

Post by didit »

I put few 6.5V Recom 78xx switching regulators on a recent Digi-Key order. Hope is, they will work for specifically this. The virtue is high efficiency (~90%) and relatively clean DC. With the sort of dissipating analogue regulation discussed in this this thread roughly half the power vanishes uselessly as heat before the heaters get any. Have yet to try, so simply an optimistic suggestion versus confirmed experience. Working to silence hum from a 6SJ7 pentode, but when time allows.

https://www.recom-power.com/pdf/Innolin ... -1.0_L.pdf

Best .. Ian
Ten Over
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Re: 7806 heater issue

Post by Ten Over »

martin manning wrote: Mon Dec 25, 2017 12:25 pm That circuit needs a volt or two of headroom too, for the 390R Resistor and Vbe drop. I like RG's suggestion to find out what the VI characteristic of the doubler supply is, and I'm betting it won't provide the required current, but it's probably ok for one tube. There's a resistor missing from that scheme too, see below (and better yet, replace that with a 6.8V Zener, as discussed recently in another thread).
My capacitance multiplier was designed without the luxury of a winding with more than 6.3V. Therefore, the components were specifically chosen for their low voltage drops at the necessary current. The D4SBS4 bridge actually drops slightly less voltage that a bridge made from Schottky diodes. The 2SD1815 has the classic 0.6V Vbe drop. There is no need for a resistor from the base to ground in my version because I am not starting off with a voltage that needs a voltage divider. The 100r resistor drops 0.42V using the Base current which puts the Base at 6.77V, so a 6.8V Zener wouldn't be functional.
bal704
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Re: 7806 heater issue

Post by bal704 »

To put a conclusion to this topic......

I have quite a few 6SN7 and 6SL7 tubes, with a few that have a bunch of hum. I tried my 'gold standard' to rule heater problems in or out, which is lifting the heater string to the preamp tubes and attaching the string to a 6V lantern battery. On the noisy tubes, the hum vanished. However, most of the tubes I have don't have the hum problem.

In the end I just went back to the AC heaters, and cherry-picked some tubes. As a side note, these octal tubes sound fantastic in a pre-amp.
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FUCHSAUDIO
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Re: 7806 heater issue

Post by FUCHSAUDIO »

How big are the caps in your doubler ? I'm running 3 12AX7 on a 7806, chassis mounted ( you DO have a heat sink, yes ?), with no issues. That's almost an amp of draw....
Proud holder of US Patent # 7336165.
bal704
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Re: 7806 heater issue

Post by bal704 »

100uf/50v on the doubler.
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martin manning
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Re: 7806 heater issue

Post by martin manning »

Increase the doubler caps to 3300u to 4700u and I think it will work, but you will need over 3A from the 5VAC winding.
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FUCHSAUDIO
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Re: 7806 heater issue

Post by FUCHSAUDIO »

I'm running 2x6800 for each of the doubler caps . There you go...
Proud holder of US Patent # 7336165.
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