Valve Jnr EL84 bias..

[grandmasterflash213]

After performing many mods on my VJ, im still dissappointed with the overdrive it produces. After a few resistor changes, the EL84 plate voltage is now just over 300v and the dissipation just over 12W. The amp sounds produces nice clean tones but the overdrive is still quite harsh and raspy. Is the tube bias still too hot? I read somewhere that the max plate voltage for class A operation is 250v, should the value be brought down to this in the VJ? is harsh overdrive a characteristic of output tube biased too hot?

[steve]

After performing many mods on my VJ, im still dissappointed with the overdrive it produces. After a few resistor changes, the EL84 plate voltage is now just over 300v and the dissipation just over 12W. The amp sounds produces nice clean tones but the overdrive is still quite harsh and raspy. Is the tube bias still too hot? I read somewhere that the max plate voltage for class A operation is 250v, should the value be brought down to this in the VJ? is harsh overdrive a characteristic of output tube biased too hot?

I've scratch built one amp using the VJ circuit and modified two production heads, my own personal amp and a basket case project I ressurected. In all three amps, the plate-to-cathode voltage is about 300v and the dissipation is about 12w. All of them sound great to me.

Furthermore, a few years ago I built the AX84 P1 rev. 10 amp using a tube rectifier to knock the voltage down. I believe I was getting around 260v or so using a 5Y3. It didn't sound good that low. When the tube recto was replaced with SS diodes, the amp really came alive. The new plate voltage was 300v and the tube was biased at 12w.

http://www.diycustomamps.com/valvejunior.htm

What mods do you currently have in your VJ? Preamp? PS? Power amp?

Have you changed out the OT? The stock unit sounds like crap to me. I've personally tried the Hammond 125ESE, 125CSE, Fender Champ 12 OT, and a Heyboer OT purchased through Dobermanamps.com. All were a vast improvement over the stock OT with the Heyboer sounding the best with the 125ESE not far behind.

steve

[grandmasterflash213]

Thanks Steve,

I've done the full marshall gold mods from 18watt, changed the OT to hammond 125DSE, playing through a 1x12 celestion G12H. It is pretty sweet sounding, i guess im just expecting it to sound exactly like an AC30 or something. I just clipped out the 1000pF bright cap i put over the R6, in between the two valves, and after this it sounded better to me. Im just playing around with the preamp cathode bypass caps to fine tune it, i just want a good full roar, not too much high or low end.
cheers

[steve]

Thanks Steve,

I've done the full marshall gold mods from 18watt, changed the OT to hammond 125DSE, playing through a 1x12 celestion G12H. It is pretty sweet sounding, i guess im just expecting it to sound exactly like an AC30 or something. I just clipped out the 1000pF bright cap i put over the R6, in between the two valves, and after this it sounded better to me. Im just playing around with the preamp cathode bypass caps to fine tune it, i just want a good full roar, not too much high or low end.
cheers

In that case, it may be that you just don't like the tone of EL84 tubes in Class A, SE operation. Not everyone does.

While I like the sounds I get out of the VJ amps I've modded, I much prefer the tones of 5F1 or 5F2-A SE 6V6 circuits, FWIW.

steve