Gut Shots of the Hornby Skewes Treble Booster

[Khas Evets]

From eBay. I don't know if it's original, but it's worth a look.

http://cgi.ebay.com/Hornby-Skewes-Treble-Booster_W0QQitemZ7422000502QQcategoryZ41416QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

[markm]

Interesting.
I always thought these would have had a higher component count for some reason.
   MarkM

[Dan N]

Looks different from the one we saw on this board way back when. There IS an input cap and the transistor is just a silicon PNP (if it's a 2N4061 as in the photo)- not an fet. Maybe there were different versions?

Thanks for the link!

[R.G.]

I read this with some interest. I did a layout for what purported to be the treble booster based on what little info I had.

I did get to reverse the zonk machine, and I'm pretty certain that I got that one right. But the boost was based on info someone else provided.

I have no doubt that what's shown on ebay is an original unit. But that is NOT a 2N406 transistor. Transistors that early were TO-1 metal can transistors, as shown here:
http://semiconductormuseum.com/MuseumStore/MuseumStore_2N406_2N109_Index.htm
The plastic TO-92 package was much later.

I can't tell what the actual device was yet. I'll poke at  it a bit.

[cd]

I thought that was just a typo.  Isn't it supposed to be 2N4061?

[R.G.]

Could be. I downloaded the pics from ebay and used the magic of photo software to balloon them up.

It could be a typo. Could be an honest mistake, as the "1" seems to be right on the edge of the curve of the package.

TI did make a 2N4061. It was a PNP in a TO-92 case, and it was in the 1967 databook, so it was available at about the right time. It was specified as a low noise amplifier device, good if you're making treble boosters.

More eagle-eyeing on the photos.

Two resistors and a cap have unambiguous values. The big electro is 80uF and the two resistors are 3.9K and 62K. Those match two values that would logically be close together on the board from the old schemo.

The old schemo had no input caps or output caps; however, there are clearly in and out caps here, flying off the board on leads. The flying caps are marked in "pf", "x00pf" in one case. The other cap looks comparable if not identical. There is at least one other resistor lurking under some wires, I can see the lead. There is a 100K pulldown resistor mounted on a jack.

All of that is compatible with the previous schematic if we assume that the "2N4861/2N4561" from the other schematic is really a 2N4061.

There is a black lead that could plausibly be a black battery clip wire leading to the PCB near the confluence of the 3.9K and 62K resistors. That fits with a PNP 2N4061.

Tracing wires from the jacks and switches:
A blue wire runs from one jack to the middle of the DPDT switch. This could well be the output jack wire
If it is, the DPDT switches it to either a candy-stripe wire from the other lead (bypass) or one of the off-board caps (effect?). Non-true bypass, but that was common.
The 100k pulldown, if that's what it is, is on the input jack, and that's where I'd put it if I only used one.

The red battery clip wire (??) is switched to a green wire going to jack ground when the switch is in the effect(?) position, providing power in that setting. There is a green wire
running from there to the board, which could be providing ground/power to the board.

So this photo seems to be consistent with the previous schematic if you replace the device with PNP silicon bipolar and assume that the previous schemo was made from the circuit board only , not the rest of the pedal.

It would even act like a treble booster, which was what always bothered me about the previous one.

So we only have to hypothesize two resistor values as being the same as the previous schemo to have the thing complete.

[Khas Evets]

Before we make too many assumptions, I just noticed that the seller bought some mullard caps off eBay (and there are many other older auctions from the same seller). I can't tell if they're the same as in the pedal.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4662&item=7622437269
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4662&item=7622437200
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4662&item=7622437017

He also bought some other caps:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=45620&item=4631137604
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=45620&item=4631122491

It's possible that he tried to fix some of the problems of this pedal with the offboard components (probably using GEO as his source). Also the pull down resistor doesn't have the same look as the other resistors.

[markm]

Interesting. 

[Dan N]

There's a small inside pic in this thread:

http://www.diystompboxes.com/smfforum/index.php?topic=23633.msg287368;topicseen#msg287368

The transistor looks more like an OC case. The in and out caps are present.

I can't find the original post about the one traced here. Wasn't it Ammscray?

The seller seems to be into electronics. Good for him!

[jonathan perez]

hah! go figure...but does it REALLY change too much of the sound?

[R.G.]

There's a small inside pic in this thread:
http://www.diystompboxes.com/smfforum/index.php?topic=23633.msg287368;topicseen#msg287368
The transistor looks more like an OC case. The in and out caps are present.

Ah. I hadn't seen that one.

Hey, what about this line of reasoning?
- the first HSTBs are made with PNP germaniums
- the noise, drift and general unreliabilty of GE make the maker unhappy.
- they change to a more reliable silicon PNP

Or possibly they were all PNP GE and someone repaired the unit shown on ebay with a silicon PNP.

In any case, ... it sure seems more like a rangemaster now than it did when we thought it was only a JFET with no in or out caps. At least now it's a treble booster.

[lovric]

i speculate from the seller's words :
'One 2N406 Transistor as per the original schematic with 2 Mullard/Phillips C280 Caps. Perhaps the original electrolytic is a bit dry, as in all these older pedals, but best not to replace it yet!  This version of this pedal is never seen ...'
that he repaired what was left from the original box deciding not to change the 80uF electrolytic. i distinctly see the 2N4601 mark on his photo.

electricaly the input cap that is around a couple of nF and various Si PNP transistors that are suggested replacements for 2N4061 (BC 213, BC 258, BC 308, BC 558, ++) dont make much of a difference. i have boarded it and with different input caps in mentioned span and different Si and Ge PNP transistors all give a booster. a treble booster. and, here is the shot from the simulator.

marin

[Ammscray]

There's a small inside pic in this thread:

http://www.diystompboxes.com/smfforum/index.php?topic=23633.msg287368;topicseen#msg287368

The transistor looks more like an OC case. The in and out caps are present.

I can't find the original post about the one traced here. Wasn't it Ammscray?

The seller seems to be into electronics. Good for him!

Yes, Ammscray here...I did the scheme that I sent to RG like 100 years ago...

I was given that box by somebody who told me it worked before with what was in there at the time (with no input and output caps) and took his word for it, and went from there...now we know there ARE in fact input and output caps...

I e-mailed the ebay guy and he told me the input mustard cap is 1000pF and the output mustard cap is .022 and they're both original solder joints...

I soldered up the original board that I still have with the new caps (sans 100K resistor though) and it bascially rolls off the bass a bit and doesn't sound very good...like the ebay guy says, it doesn't boost any gain

Plug your rangemasters in if you want the real deal

forget about this thing, I never heard one HS pedal I ever liked anyways

[R.G.]

OK, that's useful. That fills in more of the values.

If the caps are as noted, the simulator says that it has 0 db (unity) gain at about 2.6kHz. As it sits, the gain climbs to 22db ( a bit over ten) at 50kHz, which doesn't help us audio guys much. It's a bass cut with a vengeance. On top of that, it's low impedance at its input, so it sucks treble where it's trying to boost it.

Subbing in a choke and a resistor to fake the pickup's source impedance , the gain peaks at +14db at 5.6kHz, after which it falls off again.  Low E at 82 Hz is -53 db... it's not even there!

I'd believe that it's not a great sound, except in certain conditions. But it is an interesting piece of electroarcheology.

[JHS]

As far as I know, the early versions use a GE- trannie that HS replaced it with a FET on the later ones.

JHS

[phaeton]

I'd believe that it's not a great sound, except in certain conditions. But it is an interesting piece of electroarcheology.

Well, you know.  Sometimes a disgusting sound just what you need. 


You never know when all these crummy old circuits will become 'new' again.  In the 1980s, there were bands that wrote songs around guitar solos.  We might next see bands that write songs around guitar tones.....

Oh wait....

[Gus]

Ammscray

   Good to see a post of yours.  I just started hanging around again. been building tube and solid state condenser microphones needed a break so back to effects and amps.

[R.G.]

As far as I know, the early versions use a GE- trannie that HS replaced it with a FET on the later ones.

It was my opinion based on the schematic that I got, the pictures here, and a very few notes I've seen that the early ones may have been germanium and changed to silicon. I haven't seen any evidence to support JFET versions, except the first schemo I worked from, which we now believe to have been wrong.

When you say "As far as I know" can you describe the information that you do know? That is, if you have any information that says (a) the early ones definitely were germanium PNP and (b) the later ones were FETs?

I'm just trying to run down information.

As far as I know, the moon may, in fact, be made of green cheese... 

[JHS]

I stumbled over an interview with H.C. Meiser, owner of BSM and a RB maniac, a few month ago in a mag.

They analysed the HS originals and used them for sound reference. Acc. to him the very early units were made with Ge-trannies
and the later ones with a FET. I found the same info on a site from an english amp collector and on a site from an FX-collector.

But there are even more differences in the HS-TB. Most units were made for the use with the Zonk Machine w/o I/O-caps and FET, only a few were made as stand alone units w I/O-caps.

Acc. to Meiser RB used three to six units wired parallel (w FETS)  'cos one unit can't deliver enough output current to drive a longer cable. Maybe that' was the reason to drop the FET on the Stand alone units later.

The FET unit, a Strat and a Marshall Major produce that early RB rhythm tone.

The lead tone can't be copied, acc. to RB's guitar tech all Strats have are modified w a master Tone  with a custom made passive RCL add on, something similar to the Lawrence Q-Filter, producing the sweet RB lead tone when the tonepot is completely closed.

JHS

[jonathan perez]

i just found the site with blackmores custom tone job...but i cant remember!!!!

anyone know what im talking about? he mods guitars, amps and so forth?