Ed

[Paul Barker]

I have a pair of silvered AEG st shaped like RFT. The base is unknown to me. The vade mecham has the pinout. There are 6 pins all around the perimiter equilaturally placed and equal size. There is a locating ridge right along the base of the valve. The pin centred there is anode, filaments either side, next two pins nc top pin is grid. No idea what base is called, unlikely ever to find one. So I’ll make a a pair.

Yes now Ive found them, looking for 807’s. Came up trumps. They look nos.

Vade mechum and Franks tube data for rft Ed has the basing but not the name of it. Bound to be European. But never seen it before. Not British.



I have one ad1 with the loctal base and another with a px4 base. Both structured differenly inside too. I was going to build with those, but I thnk I’ll build with these Ed’s as they are equal.

Might take a long time though!

[Paul Barker]

Same data as PX4

[Paul Barker]

I have no idea why that multiple posted!

[rowuk]

I found this in my documents:
Socket: Telefon 7-pin (G7K)

Ed socket.jpeg (6.43 KiB) Viewed 3383 times

it seems that this valve was used for telecommunication.

[IslandPink]

Interesting. i hadn't realised that there was a relatively high power on of those German triodes. I know Jono had worked with a few like Aa and Ba ( was it ? ).

[Paul Barker]

That looks right with a 7th central pin.

[Paul Barker]

[Paul Barker]

Every day a school day. Only 2 watts dissipation. Aa looks interesting with a mu of 30.

Just seen the Ed has slightly more of all three capacitance than the px4. Not worried.

[ed]

very pretty, and the right name as well...

https://www.worthpoint.com/worthopedia/ ... -118614016

[Paul Barker]

Yes to name. Plate looks like Px4. Mine are same shape but silvered so cant see structure.

But the 3 input capacitances are a little higher than PX4. But same electrical characteristics. Get 4watts at 300v.

[Paul Barker]

Mark, I’ll use D3a as a pentode, did you use 150v anode, regulated 150 screen? What current and what resistor to bias right, and what resistive anode load please? As rcL i.e. grid choke, coupled will it drive an Ed or to I need a tube buffer? Thank you Mark?

I could drive add drve after the D3a pentode gain stage with a Hammond bifilar choke with a 10Y.

I’ll heat 10y with ac and whichever is greatest put a stephie hum injection sampling circuit to null the difference. Probably on the driver. I could have used a px4 driver, but thought better to bring the 10Y’s for a different character.

[IslandPink]

Oh blimey, I haven't got the data to hand for that.
On my 300B amp I used C3m and then 4P1L as pentode drivers. (Also EL84 on the 2A3/6B4G SE).
Oh earlier I'd used the 6GN7 I think. The gain was too high though.
You don't want too much transconductance if you have a supply over 350V because you have to burn a lot of volts in the anode resistor to get the pentode's Va down, so the dissipation isn't too high. Then you end up with an insane gain from the S x R(load) Now it can all change if you have a different voltage for the driver supply ; however you still need to swing a fair amount of volts so you can't go too low.
One rule is that you use G2 about 2/3rds to 3/4 of the voltage of the anode. That came from Thorsten and I confirmed it to myself.

For 300B I think I had 11k load and about 17ma on the C3m, like Thorsten.
Nowadays I have around 7.5k on the 4P1L with nearly 30ma current.
I believe I have had 150 on G2 in both cases ( VR tubes ) .
With 4P1L you need the proper filament supplies from Andrew ...

So D3a could be troublesome.

[IslandPink]

ps. you don't have to have the Zout ( ie. the anode resistor ) very low, if you have enough current in the driver.

pps. anodes on my 300B drivers are around 220 to 230V.

[Nick]

ps. you don't have to have the Zout ( ie. the anode resistor ) very low, if you have enough current in the driver.

Not sure I understand that, the Zout is the Zout irrespective of the current. Though in practice high current will tend towards a lower value anode resistor (unless you have a lot of B+ to deal with).

B+ = 250, Va = 150, Ia = 10ma, RA = 10k
B+ = 1000, Va = 150, Ia = 10ma, RA = 85k

In both cases you have 10ma, but in one case the Zout will be 10k the other 85k (well a little less in both cases as the Ra of the pentode is not infinite). Of course you do need enough current to drive into the capacitance and grid leak of the driven valve but as long as you have enough current I would have thought the Zout would be the thing that was controlling slew at high amplitides.

[Paul Barker]

Ah, thank you Mark. Sounds like I should go 4p1l at 30mA in one stage. Dont have any c3g thah knaars. I have Andrews boards somewhere…….

I’m struggling to remember when I bought these Ed valves. But Im pretty sure it was early on at one of the radio rallys and they were cheap because the seller saw them as junk. Probably paid a fiver each.

I know I didnt buy them at premium from a valve dealer. I bought PX4’s from Jim Fish and the National Vintage Radio thingermejig @£60 each. That price was a good discount from a dealer in those days, hed probably have listed them at £80 those days. At same show bought two 4212’s for £200 each I think. Shame I wasted so much time and money on 212, 4212, a300, v1505, in those days. Only to find out later the 833 absolutely knocks them out the park. Maybe I should travel to Japan with them in a chest to sell them……