DIY DUAL GERMANIUM MIC PRE-EQ BASED ON NEVE EARLY DESIGNS

[API]

akward... i dont see any of these 10M carbon resistors (on the lowcut rotary) in the schematic. anyone have an idea? are these used to  supress pops when using none-shorting swithes maybe? they are also present on the low freq switch but not for presence.

looking again at the gain rotary id say its non shorting.... hard to tell

I dont realy understand, the 10M are both on the schematic and on the switch.
The switch you posted a pic of is the gainswitch.

 

[API]

well i honestly dont know. dont want nasty clicks when switching. i guess ill just try a none shorting one first and see how it goes. ill report back

I did measure and can report that the gainswitch in my 1061 is non-shorting.
Not sure if that is better or worse than a shorting one though.
If i just think about it a shorting would be "better", but i doubt it makes any major difference.

 

[salomonander]

I dont realy understand, the 10M are both on the schematic and on the switch.
The switch you posted a pic of is the gainswitch.

hey API,
im talking about the switch to the right of the gain rotary. i marked the resistors (scroll to the right of the photo) - i dont see them on any schematic. im pretty sure that they are used to supress clicks.

 

[salomonander]

I did measure and can report that the gainswitch in my 1061 is non-shorting.
Not sure if that is better or worse than a shorting one though.
If i just think about it a shorting would be "better", but i doubt it makes any major difference.

so my eysight did not fail me thank you so much. i really appreciate your patience. and i stand by my word - pm me your adress for a bottle of wine!

 

[salomonander]

ps: found some nice rotary switches for the gain switch. centralabs pa2012 (ceramic) or pa1014 (phoenolic). they are still available through some surplus. they are shorting - but i guess that wont hurt and none shorting ones are available as well. they look just like the original ones.

ps2: i realized that the carbon compound resistors are all marked on the original schematics. not on tekays redraws. actually its the other way around - the small ones are marked as MO (metal oxide). i assume its safe to replace those with metal film.
are you guys able to tell what wattage the big carbons are`?

 

[salomonander]

alright. having the gardners remade isnt cheap. i got a quote of only 300 pounds a piece when taking 10+ ill not get any...

 

[API]

I could have told you that 
You are not the first one to ask, i think there is another thread somehwere about it.

They are plenty and quite cheap on Ebay if you keep your eyes open.

 

[salomonander]

I could have told you that 
You are not the first one to ask, i think there is another thread somehwere about it.

They are plenty and quite cheap on Ebay if you keep your eyes open.

if you find a source (for mu2526 especially)  lease let  me know. i dont see them on ebay often anymore. and i do check every other day literally....

one more question if you guys dont mind. i want to be as close as possible to the orinal. therefore use carbon compound in the according places. telling from the photos neve used 1W resistors... do you guess such a high rating is really needed?
i doubt it personally but im no expert. 1/2W carbons cost a fraction - do you thing they'll do the job?

 

[salomonander]

Ian was nice enough to clear this up. those big carbons are old Erie resistors that did not conform to standard sizes. they were basically all the same size up to one 1W. so these are most likely 1/2W just as the metal oxide ones.
he also confirmed that the 10M resistors were used to prevent clicks and pops.

would any of you be able to tell what kind of HFe and leakage requirements for ac107 and nkt216 are? my ac107s all measure somwhere in the 60-70Hfe range but my nkt216 do vary massively. going from 34Hfe up to 130Hfe. i might have gotten a bad batch. im just trying to find out what ballpark value im looking for on the nkt216 mainly.

 

[salomonander]

the tekay drawings for b100 are pretty different from this scan....

 

[API]

They look very similar to my eyes...

 

[salomonander]

check the junctions of the nkt216 emitter and the ac107 collector.... but i think tekays drawing is correct.

 

[API]

Ok, now i see it, Tekays is correct and there is actually three dots missing on the original schematic.
One more in the junction of C1 and R8 as well.

Maybe they just simply made a mistake that was corrected in later revisions of the schematics.
But good spotted Salomander.

 

[salomonander]

Ok, now i see it, Tekays is correct and there is actually three dots missing on the original schematic.
One more in the junction of C1 and R8 as well.

Maybe they just simply made a mistake that was corrected in later revisions of the schematics.
But good spotted Salomander.

thanks mate. i did stick to tekays drawing.

 

[vinyvamos]

Here I go again, digging up an ancient thread.... oops! Did any of you ever bring into a being a functioning unit from these discussions? If so, how did it go? Noisy? I am assuming that B100 could be finicky!...

I am currently experimenting with  these designs, based on all these valuable docs that I found here (thanks SO much!). While I am waiting for a bunch of germanium 3-leggers to arrive, I am trying to figure out or estimate the gain that each stage gives, considering that the gain switch is at 80dB for example. I started building my unit from the output backwards, so right now I have 2x B105 doing the Presence, Bass & Treble, and a B104 driving output iron. The two B105's seem to give me 11dB of gain with all tone controls flat. Currently I have a rotary switch on the B104 which varies the R value in the R&C network between L & A. I have C fixed at 470uF. In this way I can get 3dB steps from 9dB up to 36dB (measuring the gain of this B104 plus 1:2 output trafo included).

 

[Whoops]

Salomonander and Vinyvamos,
just posting to check how did your projects go?

Were you able to finish you circuits?

 

[hans a]

Does anyone know how much gain one could get from only one b100 with input transformer?

 

[vinyvamos]

Well if you treat the voltage gain from your input trafo ratio seperately, the B100 should give you 37dB of gain. That is what I measured when building these Germanium amp blocks. Clipping point was at 175mVp-p input and noise level was less than 100uVrms when the input was strapped with a 150R resistor. I used OC44 and OC45 transistors for TR1 and TR2 respectively. Hope that helps somewhat.

 

[vinyvamos]

And sorry @Whoops for not getting back to you two years ago! I managed to build up an entire 1057 in the end, minus the HPF section. It needs more work. It oscillates at certain extreme EQ settings and the noise floor is quite high. This is possibly the hardest part with replicating these old Germ designs; getting the noise low enough. My intention is to get back to it and start trying various transistors, especially in the early stages (B100 and onwards). I will give an update here when I do

 

[Whoops]

And sorry @Whoops for not getting back to you two years ago! I managed to build up an entire 1057 in the end, minus the HPF section. It needs more work. It oscillates at certain extreme EQ settings and the noise floor is quite high. This is possibly the hardest part with replicating these old Germ designs; getting the noise low enough. My intention is to get back to it and start trying various transistors, especially in the early stages (B100 and onwards). I will give an update here when I do

thanks for letting us know mate,
I really wish you have the time to solve the oscillation problems.
If you need some other germanium transistors to try out I have some stock and maybe could help out, if you find the problem is related to the transistors