• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

First SE Amp Build

keveas

Member
2015-02-19 8:26 am
Hers my first and i would think only Amp build
why should i build another ? sounds good to me

EL84 + 6N1P

Mains transformer and output transformers salvaged from old
equipment.

chassis made by myself

the two 270R resistors in the bottom right where latter replaced with a
external Buck transformer to give the correct 220V Ac supply to the
mains transformer

finished a few months ago and as ran for hours with no problems

as this gave me a interest in valves i decided to build a valve tester also
which is now 95% complete

last time a posted i asked for a recommended EL84 circuit but got no positive
response ,

so i carried on regardless

13599


13598


13597
 

kevinkr

Administrator
Paid Member
Why is there a diode in the feed to the EL84 screen? And another one in the feed to the OPT?

Obviously a misunderstanding on the part of the original designer as to what the diode is actually doing in circuit.

I'd remove them post haste, and probably add a screen resistor of at least a few hundred ohms. I'd also add an option for triode operation.
 

Hearinspace

Member
Paid Member
2008-06-03 5:18 am
The one to the screen looks like he's thinking of Dennis Grimwood's use of the series diode + resistor for triode connection. Have you tried it switched to pentode mode?
The first post says it works and sounds good so there's nothing to argue about but I'm wondering how it can work in both modes with that orientation.

The diode in series with OT primary is something I've seen on schematics before (and in one particular case was told it made an audible positive difference - something about recovery behaviour interaction between driver and output) though the ones I've seen put the diode on the driver side of the junction to B+.

And there's a third on the connection to Left channel. . . . . . . .

Is there an explanation on the designer's web page?

Anyway , Looks good, Nice job !