What is this 6v6 doing?

[Chuck H]

Look at V5 in this schematic. 5VAC with a very high DC component on the heater? I assume it's some sort of voltage regulation? Don't know enough to understand the use of a 6V6 in this manor. But it's always intrigued me. So I thought I'd ask.

TIA

http://www.webphix.com/schematic%20h...namps/ga86.pdf

[soundguruman]

Look at V5 in this schematic. 5VAC with a very high DC component on the heater? I assume it's some sort of voltage regulation? Don't know enough to understand the use of a 6V6 in this manor. But it's always intrigued me. So I thought I'd ask.

TIA

http://www.webphix.com/schematic%20h...namps/ga86.pdf

It's called a ballast tube. Yes it's a voltage regulator. But it is interesting that they used a 6V6.

[g1]

Chuck, seems other ampagers have pondered this as well
ampage > Music Electronics > Guitar Amps : 1 : Gibson GA86 Question

[Tom Phillips]

Yep. Back in the day tubes were used for voltage regulation. (And are still used by some audiophiles).
Attached is a copy of the HP712 O&M manual. Take a look at the schematic and, among other interesting circuitry, you will find a quartet of 6L6s being used for voltage regulation.
The theory of operation section of these old manuals is very instructional.
It's worth a gander or for some bedtime reading.
Cheers,
Tom

[Enzo]

As I go through the old equipment in my shop to assess what I have and put it in good shape, I have a couple Heathkit power supplies IP17, IP32 (B+, C-, heater)in which are 6L6 based regulators. Look up voltage regulator in the RDH, they didn;t have solid state available when it was written.

A power tube is used because it has to conduct the full current of the circuit.

They ran it on the 5vAC because it needed to be isolated from ground. Otherwise we'd have 300-400v on the cathode right next to the heater. The tube will run well enough on only 5v to do the job, so no point in adding an entire 6v winding for that one tube, they just paralleled it off the rectifier winding.

[Chuck H]

Thanks all. I should have searched and checked archives, but it seemed like either an obscure or bonehead question (perhaps both). Will follow up with suggested reading.

[loudthud]

Seems to me I remember another Gibson schematic that used a 6L6 for a screen regulator with a pair of 6L6s for the output. This Guild Quantum Bass schematic Prowess Amplifiers - Misc - Schematics - Guild Quantum bass - Guild Quantum bass 8417 w 6gf7 regulator uses a 6GF7 to regulate the screens of a pair of 8417 outputs. The pass tube has an 11 Watt plate rating. The gain tube uses the bias supply as a reference voltage. Note the separate heater winding for the regulator tube.

[Wombaticus]

They ran it on the 5vAC because it needed to be isolated from ground. Otherwise we'd have 300-400v on the cathode right next to the heater. The tube will run well enough on only 5v to do the job, so no point in adding an entire 6v winding for that one tube, they just paralleled it off the rectifier winding.

If I'm reading this schematic for the Sho-Bud Compactra 100 correctly, not all manufacturers worried about this. Incidentally, I saw Deke Dickerson play through one of these a few months back, and chatted with him a bit about his unusual amp. It was (as you might expect) a total clean machine... Very loud and crisp -- ideal for steel players, or guys like Deke.

[Gtr_tech]

There's a 50w amp circuit in the back of the last RCA tube manual that uses a tube regulated screen supply.

http://www.angelfire.com/vt/audio/rca50wdia.gif