Fuzz Aldrin hfe question

L

lespauldoc

New member
Hey all--- I'm going to build the "holy trinity" of Skreddy based on other reports I saw in this forum: Lunar Module, Screw Driver, Hybrid Fuzz Driver. Yes, looks like we can build all 3 with the Aldrin board! I have the HFD, so will be awesome to compare the 3 builds to!

So easy question, maybe. What hFE are we looking for in the Si, and especially the Ge? I have tons of Soviet/Ruskie transistors so will be fun to socket and experiment.

Thanks!
 
HFE is not the important factor. Leakage is the important factor with Ge transistors. You want something leaky for Q3 in the SD & HFD to get the correct tone. I tried MP38A, 2N1308 & AC127 in my HFD. The MP38A was fairly close, but only the AC127 had the correct tone. In the end, it comes down to what sounds good to you.

I recommend building the Screw Driver first. It's tone is somewhere between the Lunar Module (Aldrin) and Hybrid Fuzz Driver. If the SD is too "hot" for your tastes, then you probably won't like the LM. Also bear in mind that Marc Ahlfs (Mr Skreddy) designed the LM & SD to work best with single coil pickups and the HFD was specifically designed to work with Humbuckers. Doesn't mean that you can't change it up. It does mean that the LM & SD are more bottom-heavy.
 
Chuck D. Bones said:
HFE is not the important factor. Leakage is the important factor with Ge transistors. You want something leaky for Q3 in the SD & HFD to get the correct tone. I tried MP38A, 2N1308 & AC127 in my HFD. The MP38A was fairly close, but only the AC127 had the correct tone. In the end, it comes down to what sounds good to you.

I recommend building the Screw Driver first. It's tone is somewhere between the Lunar Module (Aldrin) and Hybrid Fuzz Driver. If the SD is too "hot" for your tastes, then you probably won't like the LM. Also bear in mind that Marc Ahlfs (Mr Skreddy) designed the LM & SD to work best with single coil pickups and the HFD was specifically designed to work with Humbuckers. Doesn't mean that you can't change it up. It does mean that the LM & SD are more bottom-heavy.
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I'll build up the stock first (Lunar) then the Screw Driver.... they already are done up with sockets for the Ge parts. I have a HFD I bought from Skreddy around 2015, so will be interesting if I can get close tones with that mod.
Just playing around to see if there's a ballpark before I just plug and play. But I'll plug and play :)
 
I too have a Skreddy HFD. I traced it and built a replica on an Aldrin board. I hooked the two up to an A/B box so I could compare the tones. My A/B box has a stomp switch and no indicator, so it's pretty easy to lose track of which of the two pedals is connected to the guitar and amp.

Using an MP38A for Q3, I was able to nail the Skreddy HFD tone, but the knob settings were a bit different between the Skreddy pedal and the clone. When I changed Q3 to AC127, then the tone and knob positions matched.
 
Chuck D. Bones said:
HFE is not the important factor. Leakage is the important factor with Ge transistors. You want something leaky for Q3 in the SD & HFD to get the correct tone. I tried MP38A, 2N1308 & AC127 in my HFD. The MP38A was fairly close, but only the AC127 had the correct tone. In the end, it comes down to what sounds good to you.

I recommend building the Screw Driver first. It's tone is somewhere between the Lunar Module (Aldrin) and Hybrid Fuzz Driver. If the SD is too "hot" for your tastes, then you probably won't like the LM. Also bear in mind that Marc Ahlfs (Mr Skreddy) designed the LM & SD to work best with single coil pickups and the HFD was specifically designed to work with Humbuckers. Doesn't mean that you can't change it up. It does mean that the LM & SD are more bottom-heavy.
Click to expand...
@Chuck D. Bones I've been wandering through the rabbit hole of HFD/Lunar Module, which led me here. I am pretty new to all of this, and am curious if there are numbers around leaky or not-leaky for Germanium. In this case, what would you think of as leaky? >200 µA Ibc? at a particular collector current? I use the RG Keen testing, but modified a bit so that I can adjust the base current to a target.
 
The two leakage currents I measure are Iceo and Ices. Ices is basically the same as Icb since E & B are shorted together when measuring Ices. The one I pay the most attention to is Iceo (collector current with B not connected to anything). How much is not enough? How much is too much? How much is just right? Every circuit has its Goldilocks range. It depends on the DC resistance in the base circuit and how much feedback there is to stabilize Ic. The Screw Driver and Hybrid Fuzz Driver were designed for a leaky Ge trans in the Q3 position. I put an AC127 that had Iceo around 1mA (that's right, 1mA) in an HFD I built. It biased and sounded just like the stock unit I have. A lower leakage trans did not. I worked and it sounded good, but it did not match the production unit. The Pink Purple Fuzz will tolerate a fairly broad range of leakage and HFE. Other circuits, like the FZ-1 or Tone Bender Mk III are very picky about leakage.

The short answer is is you're building an HFD, a Ge trans with leakage around 1mA is good.
 
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