Sola Sound - Tonebender Mark II Professional  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
bhill
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Post by bhill »

phibes wrote:The AC176's sound like a cool idea. Where those fall gain wise?
Sorry I missed this and am a bit late replying. Just call it a senior moment. :oops: I could claim that I've been busy building things for the last month, but all I've done is an UglyFace. And changed out the dead and dying opto couplers in my Blackface Bandmasters. And built the old lady some frames for raised bed gardening. And moved around a ton of gardening soil to fill them. And getting the front bathroom ready to put in a shale tile floor. And... Damn, I thought retirement was supposed to be relaxing. :?

Picked up a batch of 100 of the AC176's around a year ago. Ran them through the test setup (made a quicky board last year with RG's test circuit just to save breadboard space) and the end result was a bell curve, as you would expect with that many random trannies. low end had Hfe's in the 40s, high end had a couple in the 130s but most of them clustered in the 60s to 80s. Leakage pretty much followed the Hfe values with variations from around 200ua up to a couple that were over 500ua. They seem to average around 100-150ua higher leakage than the equivalent gain AC128's I have, but with the exception of the over 500ua examples they should all be usable. The one very low leakage one in the batch with a 55ua reading only has a Hfe of 23, so I don't have a use for that one as of yet.

I really really doubt that I will end up building 75 - 80 germ dirt boxes with the couple hundred PNPs and NPNs in the parts bins, but you never know... :hmmm:

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Post by jrod »

phibes wrote:How you bias'n?
25K trim pot on Q3 collector at about 8v or so. Any suggestions?

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Post by phibes »

jrod wrote:
phibes wrote:How you bias'n?
25K trim pot on Q3 collector at about 8v or so. Any suggestions?
Yeah, stick that 8K2 back in and drop the Q2 collector resistor for a 100K trimmer or 100K resistor. I usually always get the sweet spot around half way (47K, surprise surprise) but once you get up to 100K you should get the gating. I've done that with a lot of the mullard family and usually got the same results. Upping the 10K off Q1's base to 100K can also help.
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Post by jrod »

phibes wrote:
jrod wrote:
phibes wrote:How you bias'n?
25K trim pot on Q3 collector at about 8v or so. Any suggestions?
Yeah, stick that 8K2 back in and drop the Q2 collector resistor for a 100K trimmer or 100K resistor. I usually always get the sweet spot around half way (47K, surprise surprise) but once you get up to 100K you should get the gating. I've done that with a lot of the mullard family and usually got the same results. Upping the 10K off Q1's base to 100K can also help.
Awesome! I will give that a try! Thanks! :thumbsup

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Post by bato001 »

Here is my latest MKII. Still using up the TI 1304's. I originally wired this up with shielded cable, but the only shielded cable I could get locally was stranded wire and after finishing I was not happy with the connections. I was concerned that they would eventually break. So I de-soldered all the shielded cable and replaced it with good ole solid core wire. I really cranked this thing up yesterday through an Epiphone Blues Custom 30 tube amp, and it was no noisier when engaged than when bypassed, so I am very happy with it. I am selling this one locally to finance the purchase of more transistors and carbon comp resistors.

I am thinking about ordering in some 2N2431's. Has anyone used these transistors. They are listed as comparable to AC128's. Or 2N1302's?
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PBender_worngold 011.JPG
PBender_worngold 006.JPG
015.JPG
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Post by Electric Warrior »

Scored a Sola made Marshall Supa Fuzz :mrgreen:
Here are the voltages:

Battery: 9.67V

Q1
C 9.02
B 0.03
E 0

Q2
C 0.17
B 0.08
E 0

Q3
C 8.44
B 0.17
E 0.11

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Post by phibes »

Guts EW!
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Post by Electric Warrior »

Marshall_Supa_Fuzz_01.png
Marshall_Supa_Fuzz_03.png
Marshall_Supa_Fuzz_05.png
Mustards are probably not original, I think this one came with 0.01µF caps of some sort. The piggybacked cap is also questionable. Must be a pretty old mod as it still has the original battery snaps.

Other than that it's a bog standard OC75-MKII. 10k at Q1's base, 47k at Q2's collector.

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Post by nightraven »

"bog standard" :lol: that thing is awesome!

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Post by phibes »

Damn, that's sweet! Good score EW.
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Post by DrNomis »

I just recently bought a set of 5 Black Glass OC81D Ge PNP transistors on eBay, I received a parcel card in my mailbox on monday and went to pick it up, when I got to the post off ice they couldn't find the parcel so I was asked to come back the next day which I did, it turned out to be the 5 OC81D transistors, I checked them on my component analyser and found the Hfes ranged from about 28 to 35, with leakages ranging from about 290uA to 360uA, I know they're a bit low on gain but I'm going to try using three of them to build a Tonebender Mk II Professional and see how they go.... :thumbsup

Here's a pic of the OC81D transistors:
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OC81D PNP Ge Transistors
OC81D PNP Ge Transistors
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Post by Scruffie »

Those are those new production 81Ds aren't they? Surprising the leakage is so high for such low gains.

Might be worth making 2 sets of darlingtons with them?

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Post by DrNomis »

Scruffie wrote:Those are those new production 81Ds aren't they? Surprising the leakage is so high for such low gains.

Might be worth making 2 sets of darlingtons with them?

Not sure if they are new productions, the leads do show a bit of tarnishing on them so they could very well be NOS, then again you never know, I've read reports on the internet that some unscrupulous individuals are making fakes of classic Ge transistors and passing them off as the real thing, the low Hfe readings could be due to the cold weather we've been having lately, they're germanium devices and therefore are temperature sensitive, I might try breadboarding the Tonebender MkII circuit this weekend and see how the transistors bias-up, I may well have to use 4 as darlington pairs...... :hmmm:
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Post by Scruffie »

DrNomis wrote:
Scruffie wrote:Those are those new production 81Ds aren't they? Surprising the leakage is so high for such low gains.

Might be worth making 2 sets of darlingtons with them?

Not sure if they are new productions, the leads do show a bit of tarnishing on them so they could very well be NOS, then again you never know, I've read reports on the internet that some unscrupulous individuals are making fakes of classic Ge transistors and passing them off as the real thing, the low Hfe readings could be due to the cold weather we've been having lately, they're germanium devices and therefore are temperature sensitive, I might try breadboarding the Tonebender MkII circuit this weekend and see how the transistors bias-up, I may well have to use 4 as darlington pairs...... :hmmm:
Well I think those are DSI brand, which are new production, here's a thread on them - https://www.diystompboxes.com/smfforum/ ... ic=82702.0

I've not seen any original 81D like that, as far as i'm aware the original glass package ones always came with a rubber sheath (of which i've only seen white & green).

I have used low gain transistors in the MkII, but i'm not sure they were that low, sure they'll work but not sure how MkII-y they'll be.

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Post by sinner »

I had some black glass OC81D made in holland. I took them off of broken radio

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Post by DrNomis »

Scruffie wrote:
DrNomis wrote:
Scruffie wrote:Those are those new production 81Ds aren't they? Surprising the leakage is so high for such low gains.

Might be worth making 2 sets of darlingtons with them?

Not sure if they are new productions, the leads do show a bit of tarnishing on them so they could very well be NOS, then again you never know, I've read reports on the internet that some unscrupulous individuals are making fakes of classic Ge transistors and passing them off as the real thing, the low Hfe readings could be due to the cold weather we've been having lately, they're germanium devices and therefore are temperature sensitive, I might try breadboarding the Tonebender MkII circuit this weekend and see how the transistors bias-up, I may well have to use 4 as darlington pairs...... :hmmm:
Well I think those are DSI brand, which are new production, here's a thread on them - https://www.diystompboxes.com/smfforum/ ... ic=82702.0

I've not seen any original 81D like that, as far as i'm aware the original glass package ones always came with a rubber sheath (of which i've only seen white & green).

I have used low gain transistors in the MkII, but i'm not sure they were that low, sure they'll work but not sure how MkII-y they'll be.

I'll let you know how it all pans out..... :thumbsup

By the way, I tried measuring their Hfe's with a digital multimeter set to Hfe, the readings I got were in the 60 to 75 Hfe range, but more to the point, the red dot on the encapsulation was consistently next to the Collector lead as indicated with my component analyser, so I think they are otherwise all good ones, I did the same tests with some AC127s and got funny results with them, the AC127 transistors giving funny results turned out to be useless.... :thumbsup
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Post by Scruffie »

The red dot has always been the collector on any germanium i've ever used... that's what it's for as far as I know.

Well the DMM readings are higher because of the leakage aren't they.

AC127s? They're NPN aren't they? Germanium NPN seems to commonly be of worse quality (except for some of the russian stuff and wherever Smallbear Steve is getting his NOS parts) they were probably just hugely leaky and shot.

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Post by sinner »

All npn ge's i have/had tests great - random hfe, but no leakage at all or minor

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Post by DrNomis »

Scruffie wrote:The red dot has always been the collector on any germanium i've ever used... that's what it's for as far as I know.

Well the DMM readings are higher because of the leakage aren't they.

AC127s? They're NPN aren't they? Germanium NPN seems to commonly be of worse quality (except for some of the russian stuff and wherever Smallbear Steve is getting his NOS parts) they were probably just hugely leaky and shot.

Yep, that's true, Germanium transistors do generally exhibit alot more leakage (microamps) than Silicon ones do (nanoamps), and yes AC127 transistors are NPNs, they're basically the complements of AC128s which are PNPs, in the early days of transistorised radios an AC127 and an AC128 were used as power output transistors in what's called a complementary Push-Pull configuration, sometimes either two AC128s or AC127s were used together with a small audio output transformer, I used to have a couple of OC140 NPN transistors and they had very low leakage currents, worked great in a Fuzz Face circuit, unfortunately one of the leads broke off one of the OC140s right where it goes into the encapsulation so I couldn't use it anymore, when you buy Germanium transistors on eBay it's a case of pot-luck whether you get good ones or not, and I tend to have a philosophical attitude about that and accept that I'll ocasionally get duds, sometimes you do end up scoring a few gems though.

The reason why Germaniums leak more than Silicons has alot to do with the atomic structure of the Germanium semiconductor material, the electrons in the outermost shell (the Valence Shell) aren't held as tightly in their orbits around the nucleus as they are in the Valence shell of a Silicon atom, therefore they are easily knocked out to the shell by an electric current, sorry about the technical terms there.... :thumbsup

I wonder what criteria Smallbear Steve uses for determining which Ge transistors are good or not?.... :hmmm:

I also wonder what criteria Analog Man use in his selection process too?.... :hmmm:
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Post by lowbrow »

I would bet Steve uses the method described in the GeoFX "Selecting transistors for a fuzz face" article. Or something very close to it.

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