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Looking for circuit tips for 2 matched pairs of 6C33C-B (6S33S-V)
Looking for circuit tips for 2 matched pairs of 6C33C-B (6S33S-V)
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Old 3rd August 2019, 12:46 AM   #11
gabdx is offline gabdx  Canada
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It is 'easy' to build a transformer with low inductance, low input impedance, ok ok...

but the current is massive there,

for a push pull, just by memory it is around 220ma per side, , 440 ma

for a stereo, 880ma !!!

so there the core needs to be cut and put back together... ok easy

then the windings are NEVER even , so with perfectly equal bias in a typical PP with 100ma bias total...

follow this, 1% tolerance bias resistor + 0.05% voltmeter accuracy so the bias is around +/- 1ma and with a 0.5 % winding inequality the bias could fluctuate around 1.5ma

nothing too bad,

but if the current is 400ma, the tolerance will reach 6ma, this is enough to ruin the bass response and generate a lot of harmonics, reduce the inductance too much.
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Old 4th August 2019, 06:39 AM   #12
6A3sUMMER is offline 6A3sUMMER  United States
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Well,

This somewhat unbalanced tube current problem is the perfect opportunity to use 2 Single Ended Transformers per channel to do Pseudo Push Pull (to solve the unbalance problem).

Start with 2 SE transformers; each should have very good coupling from primary to secondary. And each should have low DCR primaries and low DCR secondaries.

Connect Triode 1 plate to SE transformer #1 primary plate lead (Blue).
Connect SE transformer #1 primary B+ lead to B+ (Red).
Connect SE transformer #1 Secondary Common lead to ground, and 'common speaker output connector'.
Connect SE transformer #1 Secondary 8 Ohm tap lead to '8 Ohm speaker output connector'.

Connect Triode 2 plate to SE transformer #2 primary B+ lead (Red).
Connect SE transformer #2 primary B+ lead (Blue) to B+.
Connect SE transformer #2 Secondary Common lead to ground, and 'common speaker output connector'.
Connect SE transformer #2 Secondary 8 Ohm tap lead to '8 Ohm speaker output connector'.

The push pull out of phase triode # 1 versus triode #2 drives the reversed primary lead connections.
The output secondaries are in-phase, and aiding.
Since these are SE transformers, any unbalanced DC of the tubes does not affect the core laminations (but it would have on a true push pull transformer).

If you can follow all this, you ought to try it.
I have done this before, and it works very well.

I thought I was the first to do this, but then I was told the French had done it already.

Last edited by 6A3sUMMER; 4th August 2019 at 06:44 AM.
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Old 4th August 2019, 10:40 AM   #13
TonyTecson is offline TonyTecson  Philippines
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Looking for circuit tips for 2 matched pairs of 6C33C-B (6S33S-V)
on existing se amps, you can have the same results by using a phase inverter at the inputs and the secondaries are connected out of phase in series.....been toying with this idea for so long now...
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Old 4th August 2019, 10:35 PM   #14
6A3sUMMER is offline 6A3sUMMER  United States
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Tony,

I started with a stereo 300B SE amp.
I had a medium level phase splitter module.
I connected the module 2 phase output to the triode input/driver of the stereo amp's L and R stage.
I connected the SE output transformers as described in my Post #12
That made the stereo SE amp into a mono-block pseudo push pull amp.

One key to doing it this way is to parallel the output secondaries.
For an 8 Ohm speaker, use the ground and 16 Ohm taps; get 2x the power and the same damping factor that the Stereo SE amp had.
If you series the two output secondaries, you degrade the damping factor, and also get more 3rd harmonic distortion.
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Old 4th August 2019, 11:53 PM   #15
TonyTecson is offline TonyTecson  Philippines
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Looking for circuit tips for 2 matched pairs of 6C33C-B (6S33S-V)
i heard that the 3rd aided the bass....how true? i don't know...
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Old 7th August 2019, 01:40 AM   #16
6A3sUMMER is offline 6A3sUMMER  United States
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Start with a recording of a bass note that has a rich harmonic structure.
If that is a 30 Hz bass note, and your loudspeakers cut off sharply at 60 Hz, you will not
hear the 30Hz, and the 2nd harmonic at 60 Hz will be somewhat low in amplitude.
The third harmonic at 90Hz will be heard, as well as the 4th harmonic at 120 Hz, and 5th harmonic at 150Hz will be heard.

It is a reasonably well established fact that when our ears hear the upper harmonics (in this case spaced by 30Hz each), you will "hear" the "missing" 30 Hz fundamental.
Your ear interprets, and "tells" you that the unheard fundamental is 30 Hz.

Also, if your amplifier and/or speaker creates its own 60 Hz and 90 Hz harmonics, the (missing) bass note of 30 Hz will sound louder than it would if there was no 2nd or 3rd harmonic generated by your amp and/or speaker.

Also, our ears are limited by the Fletcher - Munson Effect.
The lower the frequency, the more amplitude you need in order to be able to hear it.

Is this perhaps the effect you have heard about, and are mentioning?

The science of sound, and the science of hearing.

P.S. I was in the PI decades ago. Nice country.

Last edited by 6A3sUMMER; 7th August 2019 at 01:44 AM.
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Old 17th September 2019, 06:39 PM   #17
Vortex is offline Vortex  Hungary
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Send a message via ICQ to Vortex Looking for circuit tips for 2 matched pairs of 6C33C-B (6S33S-V)
Quote:
Originally Posted by cnpope View Post
Would you be willing to consider an output transformerless design? There are several schematics out there using a pair of 6C33C tubes to get about 25W into 8 ohms. I've been running these OTLs for a few years now, with no problems at all.
Yes, my original intention was to build Tim Mellow's OTL amp, however the crowd is split regarding OTL operation, some say it's good or can be good, others say nooo way, again others say 6S33S tubes are not that reliable in general, so at the moment I'm thinking about some kind of classic triode design.

But if you say Tim's OTL is great and reliable for years, then I might reconsider it. So many opinions out there...
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