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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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It is currently 17 Jun 2019, 07:18

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PostPosted: 12 Jun 2019, 07:02 
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Theriotically speaking, the diode that sounds best is the one that has least change in foward voltage as current varries.
Schottky didoes have lowest foward votlage and for the same current ratings the change infoward votlage is less.


I agree in theory.
However the diodes only turn on when the supply voltage exceeds the charge on the PSU caps.
The PSU caps voltage is variable on transient demand so the current charge time is variable based on the ESR.
The ability of the PSU to supply current is a trade off between transient demand and recovery time.
Ie if the recovery time is longer than the transient demand the supply will SAG.
NB that is also mentioned in the idea of the Driver/pre tubes supply being drained via the output stage causing variable supply voltage on the driver in transient.

The switching and noise as shown by Toshiba are greater with fast response/sharp recovery. That is supposed to be the theory behind tube rectifiers. Its interesting to note that tubes have high voltage drop in the forward direction, yet some people prefer them. :confused: Its also interesting to look at old circuits running in pentode with tube rectified supplies.
It is possible to filter using HF filters, but again in theory the PSU is only supplying DC. In my experience the PSU has a marked effect on sound quality. From the point of a diode never turning off its interesting to look at back EMF from inductors including output transformers and the effect on the PSU and output tubes.

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M. Gregg

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PostPosted: 12 Jun 2019, 07:05 
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I love valve rectifiers, those are the bomb.
Always better sound with valve rectifiers, and can hear the diffrence betwen going from low grade to the high grade one. 6z4j to the 6z4q or t ones.

If I can put valve rectifiers for a 12v supply I would do it, thats how much I love them.

Well it seems like your more onto it than me in the power supply diodes and all of that. I have no idea in this area.


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PostPosted: 12 Jun 2019, 07:14 
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Its interesting to look at Guitar amplifiers.

They run in pentode sometimes for power yet they still sound warm, switch the rectifier and the whole amp changes tone. :eek:
Some circuits get round it with Grid supplies to try to remove the hash.

High current delivery and quick response time seems to be the point, but the supply is always a starting point (Bass drive)


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M. Gregg

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PostPosted: 12 Jun 2019, 18:49 
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My favroutie type of valve is the pentode running in proper pentode mode.
Even in just a pre amp you can get that large valve amp like warmth very nice.

Not sure why dudes like to run kt88 and all of that in triode mode, but I like pentodes in pentode mode


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PostPosted: 15 Jun 2019, 16:20 
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Slowly compacting the circuit.

On the HT board there is the addition of 470K 2Watt discharge resistor.
The components are just dropped in place to check out some ideas (test fit) .
The underside also contains the second transformer for 5687 heaters.
I have also fitted the main vent through the chassis, its not visible in this pic and is under the remote driver board.
I need to get some more grommets. :)
Just looking at the B+ fusing 80mA fast blow 250V AC so no problems with arc quenching.

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M. Gregg


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PostPosted: 16 Jun 2019, 00:05 
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Good progress. I like your neat approach and Kafka-esque attention to detail. are there any advantages of using the toroidal compared to EI type?

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PostPosted: 16 Jun 2019, 02:50 
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Torodial normally means less magnetic flux lekage and smaller size.

This means that less noise (flux) radiated into the ampliifer case, which the amplifier will pick up if located too close.

Hint amperes law, the sum of radiated magnetic flux arround a conductor is equal to the current inside the conductor.
If you put manetic flux arround a wire you will generate voltage in the wire

This also means that if you put current through a coil you can use it as a magnet


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PostPosted: 16 Jun 2019, 10:01 
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Woodo wrote:
are there any advantages of using the toroidal compared to EI type?


This build uses EI core with a "Flux band" to supply B+ and 6X4 heaters and a toroid to supply 5687 heaters.

The toroid is more compact and less stray flux but at the trade off of high inrush which needs controlling with inrush suppression.

There is discussion on the effect of different core types and coupling with mains bourne interference. (DC component or RFI)
For interest:
http://sound.whsites.net/articles/xfmr-dc.htm

Harmonics is another form of interference..
There are also discussions on R-core etc.
That's without looking at earthing systems and high integrity earthing.. :confused:

Regards
M. Gregg

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