Vintage SS spring reverb unit

[Toxophilite]

Ever see one of these before?
Not made by the SS though!!

It's a Keil RV-1 spring reverb that uses a gibbs tank, out of an old Electrohome organ
My brother in law calls it a transitional tube to transistor unit
It has a tube topography but with transistors
It went south on me and my B-n-law fixed it(he's an electrical engineer ex ham guy)


It works and sounds like it should be given a hot signal (after a preamp maybe)
However it crackles constantly, like a record, or a shortwave radio being tuned in
It sounds like static
My brother in law said it was just part of the way the old unit sounds, but it seems to me that it's likely something amiss
He did say he tested the caps with his LCD meter and I recapped the power supply before he worked on it
When put in the circuit of one of my guitar amps After the preamp and before the PI it works (it's a nice full reverb) but with the crackle which strangely doesn't get louder when you turn up the amp so that's a plus but it's an annoyance just being there


Any idears?
Here's a picture or two and the schematic he drew up

[Toxophilite]

Could the old caps be causing the crackle/static (which just seems to sit in the back ground.) If you turn the reverb off it goes away though, but it's not affected by the amp volume


Or is it something more likely inherent in the old germanium transistors?( which my brother in law says would be near impossible to replace with modern equivalents )

[PRR]

C8 polarity is surely drawn wrong. If that's how it is inside, C8 is breaking down which could be your crackle.

All carbon-comp resistors are suspect.

'Peers to be Germanium. Any of these may have leaked over the decades.

> before the PI

What DC voltages there? Are the caps good for it?

[Toxophilite]

You're right about C8, on the unit the negative side is attached to the transistor

[PRR]

> near impossible to replace with modern equivalents

I'd try jellybean Si PNPs. They all have ample bias. If they come up in these ballparks it will work as designed.

"Q1" Collector 12V to 24V
"Q2" Collector 5V to 15V
"Q3" Collector 10V to 20V
"Q4" Collector 3V to 10V

[shooter]

fwiw, there are germaniums out there, little pricey, but the pedal guys make more money when they say it has germanium.  I'll try and hunt down some links I have somewhere.

edit:  here's a start;
http://www.mammothelectronics.com/category-s/107.htm

[Toxophilite]

Thanks
I'd appreciate that
The original transistors are 2N2428  3PE

Hmm
Some research is needed. My lack of knowledge regarding transistors is vast compared to my lack of knowledge of vacuum tubes..which is also considerable.


I have some electrolytic caps kicking around of the right values, would it be worthwhile to recap the unit? or is it more likely the transistors?


I will be checking out the resistors this eve as well

[Toxophilite]

I found this
Claims to be an equivalent to a 2N2428

http://www.weisd.com/store2/NTE102A.pdf


Also the local electronic store claims to be able to order an equivalent at about $5.60 Can a pop which these days is about 60 cents US

[Toxophilite]

The crackle isn't so bad when you don't have it full on (though I do use my reverb that way in one solo)


I'm doing the caps anyway as I bought replacements about a year ago and didn't put them in


The reverb on this is nice and full sounding, though it could use a little more zing


Is there way that could be accomplished easily?

[shooter]

The crackle

I've found most of the time I get "crackle" it's old, dirty solder joints or pin connections.

It sounds like static

Can you change the static if you "fly" your finger over the circuit?(DON'T TOUCH )
If you get like a Theremin effect in one area re-solder, swap things and check

[Toxophilite]

I physically pushed and prodded everything with a bamboo skewer, enough top make anything react in my opinion
I also passed my hand over the components with special results, turning it over and accessing the circuit board while it's on and turned up enough to hear a good crackle makes for some exciting sonic results from the reverb pan which is hugely sensitive at that setting. Maybe I'll try another gibbs pan as I do have about 4


The only thing I notice is that on of the transistors if i touch it's metal can with a little scre driver will make an audible noise, almost like it's microphonic or I'm discharging something(though the screwdriver has a rubber handle and I'm not jumpering anything. The others don't do this


To reiterate (in case I wasn't clear)
The crackly static is constant, consistant, only happens when the reverb is on and interestinglydoes not seem to be affected by the volume of the amp the unit is plugged into(I turn up the amp , the guitar and reverb get louder, the crackle stays roughly the same) ...which to me should be telling, but i can't figure out how