RH84 and Electron stream question.

[M Gregg]

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

Regards
M. Gregg

 

[M Gregg]

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..



Regards
M. Gregg

 

[M Gregg]

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..

Regards
M. Gregg

 

[M Gregg]

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.

Regards
M. Gregg

 

[Alastair E]

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....

 

[M Gregg]

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..


Regards
M. Gregg

 

[jazbo8]

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.

 

[M Gregg]

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..

Regards
M. Gregg

 

[jazbo8]

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?

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...

 

[M Gregg]

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/2013/02/rh84-amplifier-revision-2_26.html

Regards
M. Gregg

 

[M Gregg]

However the CCS I tried is the one using the 7805 + 110 ohm. (I prefer to the Mills resistor )
Used here:
http://rh-amps.blogspot.co.uk/2013/08/rh84-ppe-parallel-pentode-edition.html
You still have a series resistor..In my case kiwame 2W
Just used with a single EL84.

Regards
M. Gregg

 

[M Gregg]

So as it stands now..

Just for interest its not far away from the standard RH rev2 parallel but its not parallel. The 47K 2Watt and 10uF 400V stabilised the image.
I'm going to keep playing (modifying) for a while.. Possible electron stream switch next..(on the back of the amp)
Just preferences I guess..
I'll look at the zener across the cathode bypass cap to see if I gain any power..in the end its still an RH just bits from here and there.
If you run the EF86 direct off the B+ you get a few issues..(without the cap)
The 110 ohm in the reg is kiwame 2W.
Input has a tantalum 1Meg 0.5w magnetic across it. Input pot 100K log is carbon...HQ.

Regards
M. Gregg

 

[jazbo8]

Possible electron stream switch next..

Have a quick read of this thread (about 3/4 way through) about the so called "electron stream" theory and its application.

 

[M Gregg]

Have a quick read of this thread (about 3/4 way through) about the so called "electron stream" theory and its application.

Well,

I started wading through the link and lost the will to live..
But I will endeavour to persevere..I guess I'll find it.

OK read it and?..I have tried it several times..SE is OK..PP AB >> wouldn't use it.

I have a switch already on a SE with Triode/pentode/ U/L /Electron Stream/ and RH ..and I can switch between with a B+ kill switch..
Guess what settings sound the best..and what sounds not so good..this is also with a CCS in the cathode.

The difference between Triode and ES is minimal ES being louder. RH sounds very similar but not as good (Zener), U/L sounds pants by comparison but does give more power than triode. Just an observational reflection on sound. Pentode gives as everyone knows a more up front sound more power.

Regards
M. Gregg

 

[jazbo8]

One more thing for you to try while you are still at it - a well regulated screen supply.

 

[M Gregg]

In post 12#

C2 is now 4.7uF 400V.

Regards
M. Gregg

 

[jazbo8]

Regulated as in active regulation, not simply a RC filter. It does require more parts, but might be worth a try...

 

[jazbo8]

On second thought, screen regulation don't buy you much in a class A SE amplifier, so...

An externally hosted image should be here but it was not working when we last tested it.

 

[M Gregg]

Regulated as in active regulation, not simply a RC filter. It does require more parts, but might be worth a try...

The capacitance change was just a tweak to the driver..

I haven't tried the screen supply yet..because I'm just playing with the EF86.<<thought about trying triode EF86..

So this is still ongoing..play thing..

Regards
M. Gregg

 

[M Gregg]

This is how it is now..

(For any interested)..

Still playing with it..but its the latest diagram.
The input 1M is tantalum magnetic 0.5W.
Cathode resistor 110 ohm is Kiwame
4.7uF is electrolytic 400V.
Schade resistors are Takman MF 2W.
1k across the output Tx terminals for speaker is 5W 1K Kiwame.
2.2K stopper is Carbon film.
Cathode bypass cap is silmic 2 100uF
The 200 ohm and 300K are RRR 0.5W. (EL84)
The 390 ohm EF86 is 2W RRR.



Regards
M. Gregg