School me on OC75's

[Snufkino]

I'm going to put together a Marshall Supa Fuzz, but have never really delved into Mk.II's so I have some noob questions... For a start, what are your preferred gain ranges for the Supa? Is there a typical average, can you go high gain and destroy worlds? Are their any reliable sources to get NOS, or am I going to have to risk ebay, or settle for a modern alternative? Are their any tell-tale signs of a fake? What do they taste like?

[peps1]

Personally (as I'm sure lots of people have different opinions on this!) start with the following as my rough starting place:

Q1 150 - 170 Hfe
Q2 190 - 210 Hfe
Q3 180 - 200 Hfe

But switching them all and finding the best combination is best, so I would suggest getting a couple more then you need, so you can play about a little.

Reliable NOS sources http://www.langrex.co.uk have them in stock, I got a hundred from them last year, was very happy with them....think they are about £7 each and for a little extra will do them for you in a requested Hfe range.

[Radiotron]

Are you sure those are the correct values for the OC75’s you use? They seem excessively high to me
I like mine in the 55-90 range. Anything over 100 Hfe is pretty rare already and I don’t usually like the sound of those in a Mk-II, but, as you said, to each his own

[PlumCrazy]

I had a bunch of Philips OC75s (they have a flatter top and large lettering). They were almost all bad and leaky. Worst waste of money ever. I'd stay away from those.

[Radiotron]

Flat tops are quite different (late production I believe)
Round top OC75's are excellent transistors, that's my experience anyway

[peps1]

Are you sure those are the correct values for the OC75’s you use? They seem excessively high to me
I like mine in the 55-90 range. Anything over 100 Hfe is pretty rare already and I don’t usually like the sound of those in a Mk-II, but, as you said, to each his own

Yeah, they are the Hfe's I use, not had a problem finding OC75's in the 200 range

Got the numbers from a old post that I believe were taken by the Captain, for a original unit I think was called "the Ex Wife" but I may have dreamed that part, or been very high at the time?

EDIT TO ADD:

Cant find the post, but printed part of the page out and stuck it in my paper folder back up of important pedal stuff...

Here is some info on my ex-wife. A 1967 Marshall Supa Fuzz.

Readings taken at 9.69 volts with a fresh 226 (PP4) cell at 25.4oC.

Q1 - hfe - 174 / ic - 0.30mA
Q2 - hfe - 208 / ic - 0.27mA
Q3 - hfe - 194 / ic - 0.23mA

Voltage on Q3's Collector was -8.95V.

[Electric Warrior]

Maybe these hfes include leakage? The Captain once published hfe measurements of a Zonk Machine that was later re-measured by someone else getting much lower readings...

I have a couple of flat top OC75s. Yup, they're gainy and they're quite leaky, but they sound just fine in a MKII. The ones that work that is. A lot of the ones I recieved were broken, but interestingly they all had the same date (?) code, so that may have been a production error.

[Snufkino]

Thanks for all the replies.

Are you sure those are the correct values for the OC75’s you use? They seem excessively high to me
I like mine in the 55-90 range. Anything over 100 Hfe is pretty rare already and I don’t usually like the sound of those in a Mk-II, but, as you said, to each his own

What do you not like about high gain Mk.II's?

[Radiotron]

Maybe these hfes include leakage?.

Must be something like that.
I use a DCA, and out of the thousands of OC75's I tested I'd say 95% fall into the 40-100 range.

Some production runs test higher than others, but not by that much.

What do you not like about high gain Mk.II's?

Personally I find I don't get a wide range out the attack pot with gains high as that,
also, I just don't really care for the sound, just too much for me, kinda blatty sounding.

Again, just my opinion

[peps1]

I use a DCA, and out of the thousands of OC75's I tested I'd say 95% fall into the 40-100 range.

Genuinely interesting!

I'm sorting through a load of OC75 for some MKI builds and using my DCA here are the Hfe of what I have sorted so far (only a small sample of 88 tested so far):

0-60 = 4
70-80 = 1
90-99 = 3
100-109 = 10
110-129 = 15
130-139 = 7
140-149 = 8
150-159 = 9
160-169 = 9
170-179 = 1
180-189 = 6
190 -200 = 7
200+ = 8

Personally I find I don't get a wide range out the attack pot with gains high as that,
also, I just don't really care for the sound, just too much for me, kinda blatty sounding.

Again, just my opinion

Yes, this what it comes down to, its totally subjective, so hard for anyone to be right or wrong........MKI pedals are another one, there are some widely differing opinions on what a MKI should sound like, how much gate/decay and so on, and you just have to see Grahams videos to see the differences even in original units.