Sola Sound - Tonebender Mark II Professional [schematic]

[Scruffie]

I have built the leakage circuit, just started to get annoyed going through the large amount of tranis I have so i put it away and don't remember what I did with it, I did some more harvesting today anyway and now have some 81's 81D's 74's 71's 44's 45's 75's and i'l just socket them till I get something decent.

[Electric Warrior]

very cool. If it's not too much of a bother for you, could you please measure the OC81Ds for us?

[Scruffie]

Well I can check them now for just hFe not leakage, but i'l have to build another leakage circuit unless I find my old one to check there true hFe, but I will do it tommorow and get them up, unless you want the multimeter hFe which I can just do now. By the way Mullard OA70 Diodes any good for anything? got a couple of nice ones during my harvesting too.

[yeeshkul]

Multimeter Hfe is - in case for Ge trannies - completely useless value. The leakage current makes it all confused. It would be nice if you can provide the real Hfe because these 81D's are pretty rare these days. Are they old pieces or remakes? If they are really that weak then the "81D resistor changes" make sense.

JHS: thank you for the information on the Pagey's unit. Where did you get that?

[Electric Warrior]

Multimeter Hfe is - in case for Ge trannies - completely useless value. The leakage current makes it all confused. It would be nice if you can provide the real Hfe because these 81D's are pretty rare these days. Are they old pieces or remakes? If they are really that weak then the "81D resistor changes" make sense.

funny, David thinks they use 100k resistors because 81Ds were higher gain than the 75s: http://dam.10.forumer.com/viewtopic.php ... ight=oc81d

Scruffie wrote that his are Mullards, so they are old.

[yeeshkul]

The 10k/100k res is there because Q1 has to bias itself somehow. As you can see there is no DC voltage coming to the Q1 base. All right? Well, it biases itself due to its own leakage. The bigger the resistor is the more bias voltage you get on the base i suppose. And that supports the fuzz later in the circuit. Leakage often follows Hfe. Correct me if i am wrong. Anyway, this was discussed couple of times at Aron's.

[Electric Warrior]

Leakage often follows hfe? Yes, but on the other hand I have some very high gain Mullards that don't leak much. I expect the 81Ds to leak much less than my 75s (these have plenty of leakage - I guess that's why they work well in that circuit?). Looking forward to Scruffie's measurements

[yeeshkul]

Sure, let's see what Scruffy comes with

EDIT: "I guess that's why they work well in that circuit?" i guess that's why they work well with just 10k on Q1 base.

[Electric Warrior]

I guess that's why the OC75 version had 10k there

[Scruffie]

Hey again, right my Mullards are properrr old, I harvested them out of some manky radios full of dust, but they are tested as working on my trani tester, but I have a terrible hangover so wont be testing there hFe with leakage till later this evening, so you'll have to wait a bit but on the multimeter 100ish (90 - 140 probably) hFe rating.

I shall also give my 81's withoutt the D's to compare and see if thats where the misconception comes from? I think im right in saying the D's were drivers for the low gain 81's but I may also be wrong in saying, but we shall find out in a few hours.

[slim_blues_boy]

I tried the OC75 'configuration' with my previous TB project.
and it's work better .
this time I'm able to reach 4v with 20k trim.
I looked for my sweet spot, and stop on around 6v on Q3 collector.
roll down the guitar volume, I can get Jimmy Page type sound.
and if need more fuzz, just crank the volume guitar to full position.

I read recent discussion above.
and I also wondering which one is true, 10K is use because lower hfe transistor (OC75 has lower hfe than OC81D), or 10K is use because higher hfe transistor (OC75 has higher hfe than OC81D) .

so Scruffie how's the measurement result?
I also have 5 Mullard OC81D, but they are all useless, too leaky .

[Scruffie]

Well I can't find my old leakage tester and my hangover is still pretty bad so I gotta solder up a new one later in the evening so still gunna be a bit of a wait for the measurements, im hoping there not too leaky, they were wrapped in copper plate and came out looking brand new because of it, dunno if thats gunna have helped them but still, they look nice! lol

Be about 3 hours wait though at a guess...

[Electric Warrior]

must have been a wild night

[Scruffie]

It was wild... but i'm broken...

[Scruffie]

Sorry guys, I tried to solder veroboard to make the leakage tester but my hands are too shaky from the hangover, I burnt myself twice in the first minute so gunna have to wait till tommorow morning probably unless I feel a bit more like it later...

[Electric Warrior]

don't worry. we have time.
good you stopped soldering. no need to do more damage to your body..

[Scruffie]

Yea lol, shant be going out that hard for a while... but as I say shall get it done on the morrow and we can find out if it's low or high gain.

[Scruffie]

Right, built up the leakage detector, 70-90 hFe round about, although I wanna take a second reading later on, bit busy getting my Java boost up and running and wanna check I got it right, but that was the preliminary reading.

[Electric Warrior]

sweet. thanks a lot for busting the low gain myth!

[Scruffie]

As I said I will double check that as it was very rushed but I think the misconception came from the fact that the 81's had a low hFe where as the 81D was a driver for the 81 so probably had more but is never listed as having it's own hFe rating on datasheets. I did see one data sheet with an OC81N listed as 45-250 so... who knows.