somewhat rocket build..suggestions?

[johndandry]

Building into a very old Acetone combo. So far I got the preamp wired up, still have 470ohm/22k in the pi, might leave it for now just to see what it sounds like. big difference is in the Power supply and power amp. I'm going to keep the amps original P.S. design, SS recto, no choke, 2 100uf in parallel, 1.5k (but may change to 9.1..or 10k)- 32uf -8.2k- 32uf-then 10k-22uf for V1A. Another difference is this tranny supplies higher than needed voltage..so I'm looking at about 390-400v on the plates. It use to have a fixed bias..but I removed that and switched to cathode bias with (for now) a 125ohm/33uf (may raise) cathode bias. I haven't turned it on yet, still need to do a couple of things, so i don't know what the new voltage will be with the cathode bias or where i'll have to go with the bias resistor to get the bias right..Haven't thought about the cut yet..add it later. any suggestion so far, mostly as far as voltage and stuff. I am not trying to get the rocket sound, i know i won't with the platform i got..just inspired. Thoughts? Oh yea, only 2 EL84's also. I got some Siemens E84l so the voltages should not be a problem.

[M Fowler]

I use my cut control so much it is now a standard item. Really works well when you switch up guitar types such as from Les Paul to Tele.

125R bias resistor should be fine. The plate voltage is high but you already noted that. The voltage to the preamp tubes can and probably should be reduced on your dropping string.

I would leave the PI alone like you said but think about if you want the 220k plate resistor for V1 for typical Rocket gain or back off to 100K-150K for less gain, really cleans up the amp.

I like to clean the Rocket up and add the switch for bypass cap on cathode of V1b for nice gain. DPDT can have 1uf or 10uf or whatever gain you want 10uf and 25uf switched.

I also remove the 100pf on the volume pot and put it on a DPDT switch on off on.

Down 100pf middle none and up 350pf. The 500pf is too bright besides the treble cut control adds another tone modifying adjustment as well.

Mark

[johndandry]

So my voltages..
V1
p1:150v k3:1.09v p6:118v k8: .80v

V2
p1: 245v p2:150v p3: 150v

V3
p1: 227v p2: 33v p3&8: 53v p6: 228 p7: 20v

EL84s: Plate 364v Screens: 344 (K)Cathode: 12.44
145ohm cathode resistor, figures out to about 15watts, way too high..need to get a 165-200 to bring it down. got some hum but I think its cause of the way over bias. Am i going for like 11 watts or 8.5watts (70%)?
Right now sounds ok..plenty of volume haven't been able to turn it up yet but sounds like alot of gain, the tone is kinda middy, upper mids. I have a 250p cap in the tone stack, i'll change it to a 50p and see if that helps, also still no cut. The cut will also cut the gain into the poweramp right?

[M Fowler]

The cut will also cut the gain into the poweramp right?

No the treble cut control will not affect gain.

The volume control on the amp or on the guitar should be all you need to clean up a Rocket.

[johndandry]

well was getting 15watts plate dispersion with a 125ohm cathode resistor, I replaced it with a 220ohm and now I am getting 11.9 watts per tube@ 385v on the plate. Why am i having to go so high on the value of the cathode resistor to get it biased under plate dispersion? Also, may redo the power supply, right now the Screens and the PI are on the same PS. node.
Thinking of putting a 1K 10watt in place of the choke and adding another cap resistor in there so everyone gets their own decoupled PS node.

[hans-jörg]

Hi, I´m building a Liverpool these days. And will fire it up at least at the weekend (a kina christmas present).
So if I understand right: as higher your/mine plate voltage is, as higher the Cathode resistor. To stay at the right dissipation. I guess I will have 360 to 380 at the plates. The tail down as in the L* schem. Cannont expect to see what on the screens. Hope not too much.
What is a accepteble voltage for screens with 4 El84. The datasheet say 300VDC But thats an illusion .

Hans-Jörg

[johndandry]

Ok, update. I got the power supply as close as I can get it. Plates and screens are in the 385 range, bias 11.9watts but from the PI down I got my voltages almost exactly per the voltage chart. Amp is loud and top/mids are clear and sweet. The issue is low end. With the bass control anywhere over 1 or 2 the low end extends way too much in the low-low side, hit a low E string with the volume above 2 or so and the low end is boomy and kinda distorted. I haven't been able to really crank it but I know it will just mush out. Whats the best way to remove the lowest freq. lows off the amp as a whole. Via the 22uf cathode cap on 1st gain stage, lowering the .047 into the PI or lowering the .047 pair to .022 into the El84s? The amp is a 2x El84 incase that makes a difference in the voicing. One more question, What is the max value for the mid resistor in the tone section, 10k sounds good but would like to have a bit more mids....mid pot?. Thanks!!

[M Fowler]

Would only be guessing because we don't know what values you used on your tone board or tone stack and pot values.

If you followed the stock Rocket but made a two EL84 power section there should be not problem getting sweet chimmy tones not low end mushy bass.

[johndandry]

Found the problem!!! I had a .005 instead of a 500p (.0005) between V1a and the volume control. Fixed it and it sounds great!
I have to go get a true 500p, right now just have 2 .001 in series.
I still have the PI with 470ohm/22k bias and tail, what will I hear changing it to 1.2k/47k? More drive to the power amp?
Thanks for all the help!

[johndandry]

or if someone can direct me to a thread about the PI values...

And do I want a Silver Mica for the 500pf cap after V1a or a .0005 like a 715p?