Twice now I've had half a loaf, er, I mean half of the PP circuit running and actually other than a cut in power, it wasn't bad sounding. Actually the last time it happened it sounded just fine. The half power issue arose from one tube not conducting.
I've seen posts regarding a PP OT in SE applications and basically that is not feasible. But how about a purposely designed PP circuit that only uses one tube and balances the other side of the OT with an RC network?
Why? I don't know. Perhaps as a power cut. This may be the means to use a PP OT in a SE output. Can the Pentode be run Class A also under those circumstances or is the topology too different?
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Silverfox.
Half a Loaf of Kung Fu- i.e. Running half a PP to get SE
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Half a Loaf of Kung Fu- i.e. Running half a PP to get SE
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Re: Half a Loaf of Kung Fu- i.e. Running half a PP to get SE
PV did it in their valve king amps
He who dies with the most tubes... wins
Re: Half a Loaf of Kung Fu- i.e. Running half a PP to get SE
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Last edited by matt h on Fri Mar 27, 2015 3:12 pm, edited 1 time in total.
Re: Half a Loaf of Kung Fu- i.e. Running half a PP to get SE
I kinda assume it's either push-pull or it's not.But how about a purposely designed PP circuit that only uses one tube and balances the other side of the OT with an RC network?
But yes, single-ended topology that uses dual primary OT, with one of the primaries hooked to a circuit (usually a constant current source) that balances the current flow in primary and therefore performs flux cancellation, is quite "prior art". Few dedicated google searches should find a wealth of information.
Better explained in the fourth paragraph of 13.1
http://sound.westhost.com/xfmr2.htm#s131
Last edited by teemuk on Wed Dec 24, 2014 10:46 pm, edited 1 time in total.
Re: Half a Loaf of Kung Fu- i.e. Running half a PP to get SE
KOC does it in some of his TUT amps - he calls it a 'body' control. He also sells a single-ended mod for push-pull amps on his London Power site.
In Theory Only
Matt h- I'm also not sure what you're trying to do or what problem it is you're trying to solve.
This is only theoretical. I don't have a build in mind but had seen in various post on Forums, PP OT would not work in SE designs. Then this morning recalled my own experiences with half a tubes of Amp Fu.
The answers are most informative in that regard and nice to see it has been done.
Regards,
silverfox.
This is only theoretical. I don't have a build in mind but had seen in various post on Forums, PP OT would not work in SE designs. Then this morning recalled my own experiences with half a tubes of Amp Fu.
The answers are most informative in that regard and nice to see it has been done.
Regards,
silverfox.
Re: Half a Loaf of Kung Fu- i.e. Running half a PP to get SE
Silverfox,
Check out this schematic: http://mhuss.com/18watt/schematics/Vajra18Scheme.jpg
The Vajra has a PP/SE control.
Check out this schematic: http://mhuss.com/18watt/schematics/Vajra18Scheme.jpg
The Vajra has a PP/SE control.
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Stevem
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Re: Half a Loaf of Kung Fu- i.e. Running half a PP to get SE
All PP amps even if not biased for class A will output a small amount of class A power with one tube in,and even with both tubes in will make a tad more class A.
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Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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Re: Half a Loaf of Kung Fu- i.e. Running half a PP to get SE
And so they did. SFox, just think of PPIMV master volume that cuts volume to only one output tube. You still have bias current on the low-to-no-signal tube, that keeps the output transformer's internal magnetic field from being way out of balance, at least while in no or low-signal situations. I've repaired a couple - the sound is OK but by me, nothing to write home about.tubeswell wrote:PV did it in their valve king amps
Simply removing or de-powering one output tube leaves you with a fairly large magnetization of an OT intended for PP use. There's a magnetic gap built into OT's intended for SE use to minimize this. Peavey's circuit 'sneaks around' this problem in an affordable and adjustable way. No ninja nothin' needed, it's so simple.
down technical blind alleys . . .
Re: Half a Loaf of Kung Fu- i.e. Running half a PP to get SE
Well there is "A" in class AB.Stevem wrote:All PP amps even if not biased for class A will output a small amount of class A power with one tube in...
But, like pointed out, simply pulling off tubes is usually regarded as not-so-good option.
Re: Half a Loaf of Kung Fu- i.e. Running half a PP to get SE
I have a D'lite 44 that uses a pair of 6L6GC's.
One day I went to play through the D'lite and noticed it sounded a bit different, a bit anemic, not the same volume.
It was a usable tone but just not what I was used to.
Looking things over I had forgotten that I had removed one 6L6 for some unknown reason.
I didn't know the amp would even work with one tube.
One day I went to play through the D'lite and noticed it sounded a bit different, a bit anemic, not the same volume.
It was a usable tone but just not what I was used to.
Looking things over I had forgotten that I had removed one 6L6 for some unknown reason.
I didn't know the amp would even work with one tube.
Tom
Don't let that smoke out!
Don't let that smoke out!
Re: Half a Loaf of Kung Fu- i.e. Running half a PP to get SE
They do. But you basically run the amp SE with the little area of class-A bias allowed, and the OT without the air gap will hinder the performance even more. In practice, output power is considerably reduced and the OT's reliability somewhat compromised. But you can get "working" sounds out of such thing.
Re: Half a Loaf of Kung Fu- i.e. Running half a PP to get SE
Leo_Gnardo wrote:[quote="tubeswell"
Simply removing or de-powering one output tube leaves you with a fairly large magnetization of an OT intended for PP use. There's a magnetic gap built into OT's intended for SE use to minimize this. Peavey's circuit 'sneaks around' this problem in an affordable and adjustable way. No ninja nothin' needed, it's so simple.
Interesting point that I now realize as the why my malfunction didn't sound so bad:
The problem was in the tube socket. I could push on the tube to get it functioning and while setting the 'Bias' had a hard time as it kept drifting. So the tube was getting enough bias to balance half the OT at times. I think.
Thanks,
Fox.