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Old 20th August 2015, 06:57 PM   #1
M Gregg is offline M Gregg  England
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Default RH84 and Electron stream question.

I would like opinions,

What would happen if you reverse the zener diode on grid 2 on the RH84?
Assuming something like 40v zener.

My thoughts are you would end up with the same as a diode pointing towards the Grid (which is electron stream mod).

Can you see any reason the zener would ever be reverse biased to zener voltage with the one end on the B+ and the other towards the grid?

My thoughts are the zener would just work as a diode any other opinions?

With a series resistor something like 10 ohms as RH rev 2.

NB no one should attempt this its just an experimental question

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M. Gregg
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Old 20th August 2015, 08:14 PM   #2
M Gregg is offline M Gregg  England
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Its interesting,

to experiment with the voltage on the zener in the RH standard design.

If you have a harsh top end try increasing the zener voltage using standard orientation. Perhaps double just for interest..(tweak to your build)
Yet another trade off..

NB don't go lower than standard..



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M. Gregg
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Old 21st August 2015, 04:48 PM   #3
M Gregg is offline M Gregg  England
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Well,

as far as I'm concerned the RH84 rev2 zener is or can be a stumbling block.

Those that have built the rev2 should try the 2.2K resistor in place of the zener and have a listen..it looks like the quick zener mod can create some hash in the top end high frequencies. YMMV

I'm not a fan of the zener..it can make the RH sound more open but...its back to the stiff supply interestingly the U/L should be the bees knees however it is lacking. I get the impression this can be the make or break of these circuits...again YMMV. Trying to overcome the hash in the top end can be misleading..look at the zener..just to see. Some comments I have read on the internet seem to reflect this not being able to relax to the music. So I would expect conflicting reports from rev1 to rev2..

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M. Gregg
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Old 22nd August 2015, 08:35 PM   #4
M Gregg is offline M Gregg  England
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Its worth trying,

The CCS as rev2 as replacement for the cathode resistors for the EL84's.

I tried Mills resistor's and the CCS and prefer the CCS..you would think the standard resistor would be better..you also get the choice of the series resistor type with the Rev2..I tried Kiwame 2W. Again YMMV but its fun to try different things.

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M. Gregg
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Old 22nd August 2015, 11:40 PM   #5
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CCS will make most amps sound better--but at the expense of output power.

If you find that a drawback, use a zener across the CCS the voltage of which is a little above the CCS average standing-voltage.

Only time I ever used a Zener on the Screens was on a sweep-tube. Dunno why its done here with EL84 running well within its limits....
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Old 23rd August 2015, 08:51 AM   #6
M Gregg is offline M Gregg  England
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Quote:
Originally Posted by Alastair E View Post
CCS will make most amps sound better--but at the expense of output power.

If you find that a drawback, use a zener across the CCS the voltage of which is a little above the CCS average standing-voltage.

Only time I ever used a Zener on the Screens was on a sweep-tube. Dunno why its done here with EL84 running well within its limits....
Hi Alastair,

Have you tried the electron stream mod..its just a 1N4007 (pointing towards the tube) in the screen grid keeping the resistor in place..it is shown using the U/L tap on the output Tx. (I tried it with the pentode connection as well)

It sounds very similar to triode connection but with more power.

There is a lot of woffle (but its just a diode) on the site here: (3.1)
http://oestex.com/tubes/oes.html

Don't know if its just me but the RH is a weird critter..


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M. Gregg
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Old 23rd August 2015, 09:09 AM   #7
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A good read for your Sunday, I think "woffle" is an appropriate way to describe it. And no comment is the best kind of comment for the RH amplifiers.

Last edited by jazbo8; 23rd August 2015 at 09:14 AM.
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Old 23rd August 2015, 09:15 AM   #8
M Gregg is offline M Gregg  England
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Quote:
And no comment is the best kind of comment for the RH amplifiers.[/]
I do like the RH but I don't know why..

Perhaps its the FB type dunno..I think the zener is a problem it can make the HF a bit shrill..

Its interesting that many "Old School" amps used pentode direct to the B+..
Even Pye did it!

I tried this just for a fun exercise but ended up with the CCS in the cathode rev 2..Pic (and 100uF cathode cap)
Which is basically the RH84/ef86 with the 2.2K grid. Its not meant to be anything just a fun exercise..

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M. Gregg
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Old 23rd August 2015, 09:21 AM   #9
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Quote:
Originally Posted by M Gregg View Post
Perhaps its the FB type dunno..I think the zener is a problem it can make the HF a bit shrill..
Zener just lowers the screen voltage, why would it be a problem? Have you compared it with a regular resistor dropper?

Quote:
Its interesting that many "Old School" amps used pentode direct to the B+..Even Pye did it!
Do you mean the screen grid? A penny saved, it's one more penny for the shareholders...
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Old 23rd August 2015, 09:24 AM   #10
M Gregg is offline M Gregg  England
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Quote:
Originally Posted by jazbo8 View Post
Zener just lowers the screen voltage, why would it be a problem? Have you compared it with a regular resistor dropper?



Do you mean the screen grid? A penny saved, it's one more penny for the shareholders...
Yes tried the dropper..and electron stream and U/L and.. and...(they all sound different)
A bit like triode and U/L different..
Yes the zener drops the voltage as it says on the tin..but I think it has a sonic impact.

Sorry I forgot to link the CCS rev2:
http://rh-amps.blogspot.co.uk/2013/0...sion-2_26.html

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M. Gregg
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