Dc Heater Filaments And Running Relay Coils Updated: Hot Rodded Studio 15

[mickeydg5]

This amp in stock form has V1B and phase inverter V2A/B on one filter node. Then the first stage V1A is alone on the last filter node. I tapped my my new 2 stages off that last node that feeds V1A.

Were you thinking I added my two new stages to that crowded middle node?

So yes, I am going to restructure that later when I order my filter caps. I will put phase inverter on its own node, then 3rd/4th stages on next node and then 1st/2nd stages on last node.

I am considering 100uF for power tubes/1st node. Then 16uF node for the screens. Maybe go 32uF for rest of the nodes.

Yes I thought maybe you just stuck them in the middle there but was not sure. Still three stages up front with three stages following is a bit much too.
I guess ideal would be 2 | 2 | PI for node placement as you mentioned.

 

[mickeydg5]

OK. I made a clip showing where this Studio 15 is at. I left everything set/changes that I did last night. The main thing I accomplished last night was dialing in that pre MV to attenuate signal. So basically that 1MEG log pot is set at about 2 o'clock. And then I just use the original MV/PPIMV. You will hear me turn the bass pot from 0 to 10. Hardly any change. As we have discussed, it is not part of the tone stack and just basically shunts some signal to ground. Higher signal levels will give bassier tone of course.


Gain 6 Treble 5 1/2 Mid 7 1/2 Bass 0 to 10

There is not much bass adjustment.
If you remember, either here or in private, I mentioned there should be tweaks for voicing. It seems you have replaced the .0022uF(C13 2.2nF) and .01uF(C14 10nF) couplers after V1b with .022uF (correct?).
The tone stack and presence circuit will need tweaking to bring the bass forward.

Change C4 from 22nF to .0047uF(4.7nF).
Change C3 33k to in-line(series) .1uF and 10k.
Change C23 to in-line(series) .1uF and 15k, unless placing a PRESENCE potentiometer control there.
I am thinking remove your gain/volume controll(trimmer) indicating 57k after V5a.
Change your .033uF(33nF) couplers to .047uF or .1uF, whatever suits more lower frequencies.

 

[mickeydg5]

I took some AC signal readings on the Studio 15 power output running this hot rodded channel. Just used my meter at the speaker out jack. This is without the Jubilee clipper in the preamp. Without the clipper I have a huge signal swing of 45VAC at after the phase inverter at the junction of C13/C14. This is a hotter signal going into the power amp than I have even seen on my 2204. I have GT 6V6 which are a supposed old Russian 6L6 variant 6L6 6P3S. My plate voltage went up to 392V. I have them idling at 30mA each side.

My peak AC signal was: 31.7VAC into 16 ohm load output transformer impedance is 16 ohm.
31.7V X 1.98A = 62.8W peak.

27.9VAC into 8 ohm load output transformer impedance is still 16 ohm.
27.9V X 3.49A = 97.3W peak.

Obviously, this is using a voltage meter and it is voltage peaks. Input is my bridge humbucker pickup that puts out just under 300mV. I have the pickup lowered a bit to blend better with the single coil neck/middle.

Would I multiply these numbers out by .707 ti get a better average? And probably need the average numbers instead of the peaks at that output as well?

I was wanting to put the JJ 6L6 back in and do the sane test but things came up today. Will do that another day.

I am also very eager to try a pair of KT66 in this amp.

Would using a resistive dummy load be a way to measure and get a ballpark reading for output power?

Voltage reading across a speaker under load is obviously not giving me a very accurate power reading. Impedance changing with frequency.

I have a meter with averaging capability.
I also measure voltage across the speaker as well as actual current. I use those to ballpark the average power.

If you do not averaging then play normal, not hard and not soft, using average chords while writing numbers down for voltage and current. Get a bunch and then average that. Its good enough.

By the way .707 is RMS. Your meter reads RMS.

 

[RickyLee]

I am going to move the bass function here soon. I might even get a wild hair and do a Jubilee style dual ganged 1MEG pot scheme with the coupling cap function as well. I was really curious to swap it out like the Jubilee tone stack. But now that I have it sounding somewhat decent, I am not so much in a hurry on that now lol. I still have not installed my channel switching circuit. So the amp is hardwired with those extra stages in there.

So the bass function I will do but will wait on the other tone stack conversion until I can hear the original stock amp sound being switched in/out with this higher gain channel. I will then get my other stock Studio 15 out to compare to this little monster I have worked up.

I thought the amp came across well in its voicing on those two clips I posted. Thinking it would sound even better running through my Marshall Vintage speakers or V30's.

 

[RickyLee]

Ok Mickey. Let me know what you think of the tone now. I switch that 4n7 cap over to 10n about half way. The recording really does not show the difference as it is subtle anyway. I should have left it recording during the swap as maybe you might have heard it. I think I am going to go with the 10n there and try lowering that 4th stage cathode bypass cap down from 22uF to somewhere around 1uF.

 

[RickyLee]

I am thinking I need to figure these GT 6V6/6P3S as having the same impedance as the 6L6. All info I am finding states they are 6L6 equivalent.

 

[mickeydg5]

The sound of your shoe sole came in loud and clear.

When you record for comparisons use the same room and microphone placement.

It sounded good but there is a big difference from your last recording to this one and think it is because of the big human beam blocker.

 

[RickyLee]

The sound of your shoe sole came in loud and clear.

When you record for comparisons use the same room and microphone placement.

It sounded good but there is a big difference from your last recording to this one and think it is because of the big human beam blocker.

lol

Yeah, the first recordings were with my phone up on the bar and amp cranked. This last recording today was with the phone on the floor and amp volume much lower. What did I call out, 4 on PPIMV?