RH84 and Electron stream question.

[DF96]

There is a lot of woffle (but its just a diode) on the site here: (3.1)
Tubes

It is pure nonsense to suggest that putting a forward-biased diode in the screen grid feed will connect it for DC but isolate it for AC.

 

[M Gregg]

It is pure nonsense to suggest that putting a forward-biased diode in the screen grid feed will connect it for DC but isolate it for AC.

I agree to a point.

Regards
M. Gregg

 

[DF96]

To which point?

 

[M Gregg]

To which point?

About halfway..

Regards
M. Gregg

 

[M Gregg]

Looking at the Marantz 5,

I thought I would give this a go just for fun..
Its was just for interest..standard RH circuit with triode EF86.

Its true triode as opposed to the standard triode (G3 to cathode)
Thought I would give it a go to see how it sounds with the RH circuit.

This is a quick PP drawing just for a laugh..

The Marantz 5
http://www.4tubes.com/SCHEMATICS/BY-BRAND/Marantz/model5.gif

Again its interesting to try the 22V zener and the 2.2K resistor on the EL84.
Interesting to note the zener is more acceptable with the PSU mods posted by Rod Coleman. (L4/C2)

Regards
M. Gregg

 

[M Gregg]

I have just put,

a 47K in series with the 33K on the anode of the EF86 so it's an 80K anode load to bring the gain up a bit..

Just a bit more playing..

Regards
M. Gregg

 

[M Gregg]

I have just put,

a 47K in series with the 33K on the anode of the EF86 so it's an 80K anode load to bring the gain up a bit..

OK the 47K has increased to 150K (in series with 33K) in the anode of the EF86. Just a bit of fun..just trying a few things.
I'll try the electron stream diode in the triode connection for a laugh.

Regards
M. Gregg

 

[M Gregg]

Well,

its running diode enhanced triode..

I thought I would just end up ripping it out, however I am going to listen and see.
The initial impression is the bottom end warmth that the EF86 true triode creates is almost gone with what sounds like a clear mid and reduced spit in the top end. I increased the volume and its clearer at higher volume as well perhaps tighter bass?

However its early days yet as always..

The scratch diagram is just so you can see what I'm trying.
I used Glass passivated 1n4007 just because I had a couple in the box.

Regards
M. Gregg

 

[M Gregg]

OK,

For a laugh I looked at the parallel resistances (220K and 150K) on the anode of the EF86 and thought it looks like I could push the 150K up to 390K so I thought I'll give it a go..and its quite loud now with the diode enhanced triode EF86.

So at the moment the diode is staying..but its just a bit of fun to rock the house..

The 2.2K on EL84 is replaced at the moment with a 22V zener and its quite successful at the moment.
There is lots to try..

Regards
M. Gregg

 

[Alastair E]

Err--Whats the 1K across the speaker for...?

 

[M Gregg]

The 390K is overkill,

So its a mid compromise now the 150K is set at 220K.

It seems to work OK.

The output stage now sounds quite good in various modes I'm running U/L at the moment just to see how it sounds..( I never like UL so..)
The 22v Zener can sound a bit bright or harsh but it does give quite good power.

Hi Alastair,
The 1K is just there so I can try various feed back options it's just to keep it stable if there is no speaker connected by accident.
It appears on various Mullard circuits the 3-3 and 10 watt have it as standard.

I'm going to have a look at the Electron stream U/L and a few various ideas..I tried the usual cathode feedback using the secondary of the OP Tx but it didn't seem to work as well as the last time I used it.. (however I have changed the driver and might try it again just to see).
I'll probably end up with a switch for a few selections...its what normally happens..I'm a bit indecisive at times. Or perhaps I get bored..

Regards
M. Gregg

 

[M Gregg]

I'm using,

Just some fun..

1K CC in place of the 2.2K at the moment running UL and it sounds quite good..

The ES diode U/L is next up I recon..

It has quite good bass drive as well..but there are lots of ideas to try.

The U/L sounds very good which is a surprise because it sounded absolute pants before..

NB the resistor across the op Tx is a standard practice with everything I build now because the family like to change amps over and they get powered up with no speakers connected and after a few occasions they got fitted to stay.
Just another scratch drawing..

The OP connection will now be tried with various connections ..just for fun of course.

Regards
M. Gregg

 

[M Gregg]

The switch goes in..
(Miniature high insulation toggle)

Just for fun..

Scratch drawing..the RH rev 2 shows direct zener connection so I thought I would try it..( its a bit harsh)
Next test will be ES UL..


Regards
M. Gregg

 

[M Gregg]

Electron Stream UL,

Here is the electron stream output and it sounds very good. (Triode sound..)
The diode is a normal 1N4007 I just matched the forward voltage drop across the junction to give a matched pair.
I'm listening to the Beat at the moment and the bass is very good. Sound staging is also better..

You can hear a big difference between the zener (RH) and the electron stream U/L.
Scratch drawing..



Regards
M. Gregg

 

[M Gregg]

Electron Stream Triode,

This is interesting to try diode enhanced triode EL84.
It's an easy test just move the UL connection to anode of EL84.
The trouble with this is the zener sounds harsh when you switch back, however it does have more power..perhaps it might be interesting to put a rotary switch in and select resistor pentode, zener, UL, triode.. I quite like the diode triode however there is a power loss compared to the zener.

Its quite interesting that the triode ES sounds better on the EL84 compared to other tests on EL34 where the UL ES sounded better.

Again you should not switch over while the amp is powered.

Regards
M. Gregg

 

[Bigun]

Interesting set of experiments. What are your plans to try fixed bias on the output tube ?

 

[DF96]

You can hear a big difference between the zener (RH) and the electron stream U/L.

That is because they operate the valve under slightly different bias conditions.

 

[M Gregg]

The other version is,

Electron Stream pentode,
I haven't had chance to try this yet.

Regards
M. Gregg

 

[M Gregg]

That is because they operate the valve under slightly different bias conditions.

So what has changed? As discussed before there should be not much difference (two diodes in series).
Imaging is sharper..

Regards
M. Gregg

 

[Bigun]

what has changed? well, the diode will add its imprint as soon as the screen draws current, since the diode has its own current voltage characteristic. and because the screen grid is another control grid for the anode current it will have an influence on the sound.