REDD47 EF86 screen voltage ?

[PeteC]

Hi

I am almost cross posting form my preamplifier thread here so forgive me.....

but can anyone please check the screen voltage on a stock REDD47 clone ( or original ! ) and tell whet the screen voltage should be with he 390K screen resistor ?

In my 2 channel P2P build I am getting a screen that's quite a bit higher than my plate voltage and wanted to check if that's how the circuit is designed/meant to be.

Many thanks for your help !

cheers
Pete

 

[gemini86]

I know this isn't exactly what you asked for but I've found it to be fairly accurate for me with most circuits. According to a rough simulation with the grid grounded through 1M, the cathode shows 1.63V (VS 1.65v on the schematic I have), plate is at 72.5V (73V on schem) and screen is at 85.6V...(no voltage note on schematic for screen)

 

[PeteC]

Many thanks Rodney,

thats confirming what I'm seeing with my build

Cheers
PeteC

 

[My3gger]

PeteC, i can confirm that screen is a bit higher than plate in this circuit. I don't think i've seen this much difference (i'm replacing psu and can't check it now), there is also quite a bit of  voltage spread between different manufacturers of EF86.
Some batches of old Tesla can have very tight tolerances, their EF806s are showing pretty much same results as EF86s, two RFT/RWN EF86s i tried are also very good and seem to be well made. Svetlana's aren't as well made, but aren't noisy from the start. Don't know how long they last... All "NOS" Telefunken's EF86s i've seen seemed like a used tubes (some scratches and burns from heat on pins), so i wouldn't buy them for more than 10 euros. Let me know if you used JJ or EH and if they are ok. I'm really interested if they are any good in long term because good NOS can still be cheaper. You might find out that some EF86s are ok from the start, but become hissy after a few months or even days. Don't know why i love this tubes, maybe because you never know which will be good in long term. Like a girls, ya know

 

[PeteC]

Hi My3gger,
Thanks for the info .
here is what I am using for EF86 at moment - I pulled these from some old PA equipment so not sure of factory original they are "Made In Russia" marked with no other branding on them.
http://i55.photobucket.com/albums/g159/pedrocortez/FB2DD892-50FF-4466-AA5D-E71DC5B472C9-528-00000056B4B80625_zps77497569.jpg

I am looking out for a good pair of EF86s to replace them.

Rgds
Pete

 

[DaveP]

On the one I made, HT was 300V and after the 51k dropper it was 215V.
Plate voltage was 83V and screen was 100V with cathode 1.7V.
Hope that helps
best
DaveP

 

[PeteC]

Thanks Dave that's another positive confirmation - so I'm going with what I have built. 

metalwork now....Aaargh !

PS - whereabouts in UK are you Dave ?  - I'm in Leeds.
always good to locate other people really interested in this stuff. - especially valve musical/recording gear.

cheers
Pete

 

[My3gger]

That is Russian "Svetlana" or Winged C (named after Svetlana's logo) EF86. You will probably be using this preamp quite a lot, please let me know (if possible by pm) if you notice any noise or microphonics after some time. This tubes are still very cheap and it would be good to know how they perform in long term. Why would you want to replace them with other tubes if they work? I didn't notice much difference in sound between different brands and i tried quite a few. Brands i mentioned were checked for longer time, this is why i didn't write about others.
I like your sub chasis a lot. Do you have any particular reason for doing them instead of mounting tubes on L brackets and make the rest on turret board inside ordinary rack? I mean, you will put sub chasis inside chasis, so it won't be visible anyway.

 

[DaveP]

Hi Pete,
I live in Wales but work in Stevenage half the week, my daughters in Leeds.
I used two of these CPC boxes EN81249 end to end, pre-amp one side, power supply the other.
http://cpc.farnell.com/jsp/level5/module.jsp?moduleId=cpc/256377.xml

They work well for a 2u box....I fixed a plate on the front for rack mounting.







Have fun
best
DaveP

 

[gemini86]

That's brilliant, Dave.

 

[PeteC]

fabulous Dave....

I'd seen the pics on the REDD47 thread, and your build was one of the ones I'd seen that inspired me to get building my own.

Mine is 2 channels in 3U 12" deep penn elcom case - also from CPC !  I like the ali boxes idea as a solution.
Just need to do all the drilling and cutting of the chassis now.  The bit I get impatient with.....

I tracked a few things on Friday night using the preamp just rigged up on a breadboard with the PSU and it sounded great.

Cheers
Pete

 

[DaveP]

Good luck with your build Pete

Thanks Rodney, What a fool believes is one of the best tracks ever and has long been an inspiration to me, brilliant Kenny Loggins and Michael Mcdonald, please excuse the off topic.
all the best
DaveP

 

[PeteC]

Thanks Guys,


My3gger..... Thanks for the info on the EF86 being Svetlana's.  I only planned to replace them because I pulled them from some old PA gear that had been used quite a bit.  There will still be life in them yet I guess , but I will monitor them and let you know how they perform.  They do sound good at the moment thats for sure.  Time will tell.

Happto pm you with some thougts once I have the preamp racked up soon.

Cheers
Pete

 

[PeteC]

Hi My3gger,

sorry I didn't answer your question regarding the sub-chassis....
I'd seen something similar on a HIFI build and liked the idea - its saves some space , and lets me get 2 channels inside the chassis easily.

The layout means I can get in to change tubes - but also makes it easy for me to change components on the tagboard on top if needed.

Its probably made the build more complex because of the extra metalwork involved, but I quite like it.

Cheers
Pete