Harmonilux Reverb AA964???

[Toxophilite]

Awoke in the middle of the night, so what else to do but tinker


Just to make sure i understand how to wire it. I will write it out.



-Prr's version of the switch has me breaking the circuit between the .1 cap after the harmonic vibrato and the 10pf/3.3meg prior to the last 12ax7 gain stage.


-At the junction of the .1 cap and the 500pf cap that comes from the reverb circuit I add a 4.7m resistor to ground .
The junction of these 3 components goes to the one side of the switch


- the middle of the switch is attached at the 10pf/3.3m resistor going to the last 12ax7 gain stage


-A .047 cap is soldered to the junction of the 2nd gain stage plate and it's plate resistor (in this case a 82k)
A 4.7m resistor to ground is attached to the other leg of this cap. the junction of the cap and 4.7m resistor goes to other side of the switch.


No large voltages could be read at any on the switch points, though when switch to the harmonic vibrato there was a small fluxating voltage on the last gain stage side of the switch(middle)and the harmonic vibrato side.


The switch still made a pop


Though as SLuckey suggested (or something similar) when I flip the standby I of course don't get the pop...humourously I generally don't use my standby as it 'pops too

[sluckey]

-Prr's version of the switch has me breaking the circuit between the .1 cap after the harmonic vibrato and the 10pf/3.3meg prior to the last 12ax7 gain stage.

correct

-At the junction of the .1 cap and the 500pf cap that comes from the reverb circuit I add a 4.7m resistor to ground. The junction of these 3 components goes to the one side of the switch

wrong. The 500pf going to the reverb input stays connected to the bottom end of the 10pf/3.3M. The 500pf will no longer be connected to the .1µF.

- the middle of the switch is attached at the 10pf/3.3m resistor going to the last 12ax7 gain stage

half right. Don't forget, the 500pf will also be connected to the middle of the switch.

-A .047 cap is soldered to the junction of the 2nd gain stage plate and it's plate resistor (in this case a 82k)
A 4.7m resistor to ground is attached to the other leg of this cap. the junction of the cap and 4.7m resistor goes to other side of the switch.

correct

[Toxophilite]

Thanks
I wondered about that and should've asked!
That helps some
It pops less consistantly and primarily on the switch to bypass
it is a quieter pop


When the vibrato is bypassed the amps gain jumps by a HUGE amount
2 on bypass is equivalent to about 4-5 on vibrato


maybe that's why some people claim that the brown amps are often clean most of the way up the volume control?
Mine was certainly like that till I adjusted the voltage divider on the 2nd gain stage's plate

[PRR]

> When the vibrato is bypassed the amps gain jumps by a HUGE amount

By my thumb-count the vibe path has gain 0.2*25*0.5= 2.5, relative to the shortcut path.

The vibe channel has 12AX7 gain, a LOT. So the input is tapped-down 82K:22K, there's some loss in the filter, then gain near 50, then some loss in the mix network.

If vibe is weaker than direct, something is wrong. Weak vibe section? 2.2K where you think 22K?

[Toxophilite]

hmm
Well I just went over the vibrato circuit and I found a mistake
I'm pretty sure it's the only one
On the second 12ax7's joint cathodes I have a 25/22 bypass cap instead of a 2/25
I swapped a 2.2/100 in there that I had kicking around
The vibrato channel is a little louder now but still noticeably quieter than when bypassed, and that's even with the vibrato intensity turned right down(essentially off)

[PRR]

Voltages?

[Toxophilite]

V2
1 - 125
3 - 1.25


6 - 168
8 - 1.26


V3
1 - 271
3+8 - 3.03
6  273

[Toxophilite]

The original concert circuit has the normal channel joining the vibrato channel via 1m resistor just prior to the PI
Is that a load I should be simulating somehow?


Like one can do when building a one channel AB763 circuit

[sluckey]

no

[Toxophilite]

Well I discovered something unusual that has me perplexed
Since I built this amp there has been times when it has sounded great and other times when it seems to lose it's bottom end, significant volume(via the bottom end) and be unpleasantly middy.
As I can only use it infrequently at practice it's been hard to tell if I was fooling myself
I've gone around and resoldered things etc, the usual stuff


I just noticed when messing with my tagged in bypass switch that if I just touch a metal tool to any of metal leads of the plate power supply components for V1 V2 V3 V4 or V5 (pre PI). I could make the bottom come back and the amps sounds good, then I can reverse it back to bad sounding by touching it again.


It makes no sense, i's like there's something electromagnetic happening in the preamp and tremelo power supply
I can almost turn it on and off just by touching my pliers to any exposed B+ lead


 

[shooter]

I can almost turn it on and off just by touching my pliers to any exposed B+ lead

That MIGHT cause a life shorting event

Off the top, it *seems* you have a static buildup?, maybe some sort of *floating* capacitance?

[Toxophilite]

Rubber handled pliers!

[shooter]

Rubber handled

I thought that also with an "insulated" tweaker, adjusting 3kvdc,  F was I wrong

[Toxophilite]

huh?? what?..unnnnh ..sorry I just regained consciousness....yuck burned hair smells gross!

Seriously though
Anybody has an idea on this one?? It's pretty confusing to me
I've been poking at all the joints and components with a wooden stick with no luck
It's the damnedest thing!

[Willabe]

Seriously though

Yes, very serious, you need to be ABSOLUTELY SURE that the isolation on the tool will handle the voltage.

AND even then, keep your other hand in back away from the chassis to any path to ground through your body ACROSS YOUR HEART!       

[Toxophilite]

Right
Thanks very much
I understand the dangers and appreciate the concern.
Please, please, excuse my levity

I was really hoping to divert attention back to my original request for insight.

[shooter]

keep your other hand

That's why I'm still around to build , in the pinky, out the palm,
and levity is good; "what doesn't kill you...."  brings out the dark humor

I have *seen* your symptoms before, my *scrambled* memory keeps coming back to some kind of *floating* condition for the circuit in question, resistive ground/B+, parallel capacitance (that shouldn't be there), static buildup.

[Toxophilite]

Hmm
Are you referring to parasitic capcitance? or the miller affect?
like here:http://www.valvewizard.co.uk/gridstopper.html


It kind of sounds like it from the reading I've done


I wonder if it's:
A - my lead dress (though the amp is nice and quiet)
or B- a result of using the harmonic vibrato circuit in the AB763 circuit
or something else


Interestingly enough it doesn't seem to do the tonal and volume change thing wen the harmonic vibrato is bypassed
Frankly ,though it's a cool and unique effect, it is a lot more of an effect(like a phaser or leslie) I like the tremelo to just be an amplitube thing so I might be swapping in a 6G16 bias vary. ( I have a few of those cone boards, I might just make a new one and swap it in, cleaner)

[Toxophilite]

Out with the old, in with the new
Straight up vibrolux with 6G11-A bias vary tremelo now, Working great so far