Deacy amp question

[MartyMart]

..... looks like a fun little project, but I know nothing about the OC81d  !
Could I make this an NPN neg ground using normal "reverse" all the caps PS etc and
have a worker using OC140's and "something" for the OC81 as an NPN replacement ?
Is it just a higher hfe than OC71 .... or something a bit special ?
I'd like to keep it "Ge" for sure ...

Thanks,
MM.

[smnm]

OC81 ....Is it just a higher hfe than OC71 .... or something a bit special ?
I'd like to keep it "Ge" for sure ...

When I answer a post that has been hanging for a while someone usually chimes in immediately to contradict/humiliate me, but I think I'm right in saying that OC75 would be a better bet than OC71 for a OC81 substitute.
OC81Ds were used in some early Mk2 Tone Benders, but most use OC75 - boutique builders like D*A*M offer both variants.

Cricklewood Electronics have metal can (TO1) OC81s for £4 each if you're desperate, but they're diff to the D suffix ones:



EDIT(s) - short answer - yess the 0C81D is odd - info from http://vintageradio.me.uk/info/germanium.htm

Type   Pe Max mW  Vce Max   Ic mAX      Hfe
OC81        160           32            500           50-250
OC81D      160           32            20             >25
OC75         75            30            10             90
OC75         75            30            10             90

[MartyMart]

Thanks for the "tip" 
I built one as an NPN using OC140's - at the 'mo it's squealing like a pig !
I can hear a decent, but quiet crunch in there somewhere though >??
Perhaps my output tranny is wrong ( TM022 ) or backwards !
Perhaps this is a neg ground PNP deal only !

MM.

[MartyMart]

Got it working
A little quiet - sounds like 1/8th watt or less and it needs some biasing, but the basic "sound"
is quite cool !
It's so quiet that you could probably stick a jack socket on it and plug into an amp !!
Mixture of Ge and low gain Si trannies at the 'mo - higher gain = oscillation !

MM.

[mac]

I have some NPN 1W Ge, 2sd352 and 2ds72K, but I can't get any transformer closer to the specs in my city. I read here about some replacements but with higher resistance that I guess they may lower the final power.
What transformers are you using?

mac

[sfx1999]

I've been kicking myself because I threw out the perfect speaker cab for one of these.

What's been bothering me is that I have the Mullard Reference Manual for Transistor Circuits, and the 1W is regarded as the Deacy amp, yet the Deacy is 0.5W. There is an 0.5W one, but the output transformer looks ridiculous.

[MartyMart]

I have some NPN 1W Ge, 2sd352 and 2ds72K, but I can't get any transformer closer to the specs in my city. I read here about some replacements but with higher resistance that I guess they may lower the final power.
What transformers are you using?

mac

First is a Maplin LT44 , P 20k S 1k
Output is a mouser TM022 as used in the octavia.... this could be a problem !
Perhaps some large BD139's as output trannies would help ....

[sfx1999]

I thought I read somewhere that the sound came from overdriving the output stage. You might want to keep those germanium. The driver transistor may be a good candidate for substitution.

This may be a stupid question, but are you running a treble booster in front of it? Brian May had to in order to get the levels high enough.

[mac]

First is a Maplin LT44 , P 20k S 1k
Output is a mouser TM022 as used in the octavia.... this could be a problem !
Perhaps some large BD139's as output trannies would help ....

TM022 1.5k P, 600R S. Are these resistances or impedances? 

BD139 should be helpful for breadboarding and measure currents to see if Ge could work safely, or bd237 which is higher amp.

mac

[MartyMart]

TM022 1,5k P / 600r S are resistances.
I'm not running a booster yet but will try it out.
Doesn't sound bad, just V quiet !

[sfx1999]

So did you try the booster? I am interested to see how this turns out.

[MartyMart]

So did you try the booster? I am interested to see how this turns out.

It didn't help .... think that I need the right output traffo !