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Old 13th May 2013, 09:01 AM   #1361
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Hi Gingertube,

Thanks for the explanation. Just a couple more questions (i'm still learning).
1) Why use a 56R in the 6V6 shared cathodes? Shouldn't the grid bias provide the means to adjust output tube current?
2) What is the role of the 47k in the ccs for the FET?

Cheers ANdrew
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Old 14th May 2013, 12:45 AM   #1362
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The 56R in the 6V6 cathodes is not there to provide any part of the bias although it will contribute to the bias for the 2 tubes. It is there to provide some common mode feedback to the output tubes which helps reduce 3rd harmonic and other odd order harmonic distortion and also reduce intermodulation distortion. This was discussed earlier, see post #451 and onward. In particular note Sheldon's spectrum analyser plots.

The 47K is an essential part of the "ring of two" current source (CCS). It provides the base current for the current "pass" transistor and the collector current path for the "control" transistor.

Cheers,
Ian

Last edited by gingertube; 14th May 2013 at 01:00 AM.
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Old 14th May 2013, 08:19 AM   #1363
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Quote:
Originally Posted by gingertube View Post
... It is there to provide some common mode feedback to the output tubes which helps reduce 3rd harmonic and other odd order harmonic distortion and also reduce intermodulation distortion.
This is the method I used to reduce intermodulation with power supply ripple:
Replace the feedback resistor with two equal resistors in series so that the total resistance stays the same.
Now we have access to the 'virtual ground'. Measure it, it has all the power supply ripple and common mode signal from output stage.
Tieing it to ground with an elco (and perhaps smaller cap in parallel) will reduce the common mode signal reaching the differential stage. Enjoy the sound

PS: hope this hasn't been mentioned before in this long thread.
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Old 20th May 2013, 04:09 PM   #1364
fmena is offline fmena  Canada
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Default Baby Huey PSUDII Power Supply model with 5AR4 (long)

In the image below I've modelled the power supply using the 5AR4 rectifier. When I first modelled it, I got an error saying the current forward maximum of the rectifier (IFRM) would get exceeded at a certain time. Then when I changed the model to a 5AR4-Graetz the issue was no longer present. I already have in my spare part box some 600V (6A) Cree Shottky diodes.

http://www.diyaudio.com/forums/galle...php?photo=8568


Question(s) :
1) Is the 6A 600V diode safe enough to use in regards to voltage for rectifier use? ( I already have them)

2)If so ..can I place a single Cree diode in series with each plate (pins 4 & 6) of the 5AR4 rectifier and still use the centre tap of the mains transformer?

3) Or should I not use the centre tap and tie the diodes together something like this:

http://www.lundahl.se/sidor/hybrid_power.html

I know that I could only use SS diodes and not be bothered at all with the rectifier but I would like to try this and it is a good learning tool for me. At some point I will revert back to only SS diodes for rectification but I would like to see for myself if there is a difference in sound and or operation.

Thank you in advance & Happy Victoria Day Weekend
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Last edited by fmena; 20th May 2013 at 04:15 PM. Reason: picture wont load
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Old 20th May 2013, 04:37 PM   #1365
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On the subject of rectifiers, does anyone know a soviet rectifier that can supply enough power for one of these amps? AFAIK there's only the larger ones like 5C8S and 6D22, and the smaller octal ones. But no novals like EZ81 or similar, correct?
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Old 21st May 2013, 12:01 AM   #1366
fmena is offline fmena  Canada
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Default Found partial answer

Kevin Kr wrote :The 5AR4 is also noted for hot start arcing issues, particularly current production and placing a UF4007 in series with each plate completely prevents this issue and does not otherwise alter rectifier performance wrt voltage regulation, warm up delay or EMI.


(Diodes in a Graetz Hybrid
)

So if I am correct in my interpretation of the above, I can place a UF4007 in series with each plate and still use the centre tap of the mains secondary as normal for a 0V reference?
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Old 21st May 2013, 12:23 AM   #1367
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Yes,
The SS diodes in series with each plate handle the reverse voltage and prevent arcing issues in the tube rectifier and the tube rectifier blocks SS diode switching noise - best of both worlds.
Cheers,
Ian
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Old 21st May 2013, 06:31 AM   #1368
stajo is offline stajo  Sweden
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Great info. Does it matter if the SS are before or after the 5AR4 anodes?
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Old 21st May 2013, 06:36 AM   #1369
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The SS diodes need to be wired between the transformer HV leads and the tube rectifier anodes. That is, SS diodes in series with the the HV leads from the tranny to the tube rectifer anodes.
Cheers,
Ian
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Old 21st May 2013, 06:52 AM   #1370
stajo is offline stajo  Sweden
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Thanks. Then one could use a single damper diode instead of a rectifier tube for the same effect if I understand it correctly.
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