Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

A little study about two old germanium projects
A little study about two old germanium projects
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 19th June 2017, 02:38 PM   #11
DIYBras is offline DIYBras  Brazil
diyAudio Member
 
DIYBras's Avatar
 
Join Date: May 2015
Location: Parana
http://www.diyaudio.com/forums/solid...161-162-a.html

I liked the spirit of using an old amplifier. I made several amplifiers using old PCBs from commercial products.
Probably measurements for it differs from mine, due to silicon transistors usage.
__________________
Making cabinets for OLD projects (better later than never...)
  Reply With Quote
Old 19th June 2017, 02:48 PM   #12
DIYBras is offline DIYBras  Brazil
diyAudio Member
 
DIYBras's Avatar
 
Join Date: May 2015
Location: Parana
Quote:
Originally Posted by Zero D View Post
I have a portable radio that uses GE transistors that belonged to my dad from the 1960's. I remember listening to it, & it still works & sounds nice as it did. Not HiFi, but a nice sound & has bass too None of that awful tinny sound many had !

All the best with your adventures
Thanks! (sorry about late response but now I have spare time)
Very cool to know!
This remember when I repaired a old germanium-based 60's radio with a cabinet sized like tube radios. Sounded very good with the first audio stage cap open. But that are the reason why owner asks me to repair: low audio gain. I replaced the capacitor and sound become less good, but surprising for a old radio with trafo coupled stages.
Famous people here in forum love old germanium radios (Telefunken Bazzajo in John Curl case).

One thing that germanium definitely have is a smoother crossover distortion due to "semi-remote" cut-off, helping in some cases. If I measure a silicon amp with class B bias, the harmonics will spray flat until the audio board response limit, but in case of this little amp, the harmonics have decay and stopped less than 50kHz, like in high bias/low bias graph.

I have other Ge amp but is a subject for another thread in future.
__________________
Making cabinets for OLD projects (better later than never...)

Last edited by DIYBras; 19th June 2017 at 02:51 PM. Reason: Various bad spelling
  Reply With Quote
Old 19th June 2017, 03:36 PM   #13
Ketje is offline Ketje  Belgium
diyAudio Member
 
Ketje's Avatar
 
Join Date: Dec 2012
Location: Flanders
Rather like this ?
Mona
Attached Images
File Type: jpg Ge01b.jpg (26.5 KB, 112 views)
  Reply With Quote
Old 19th June 2017, 06:27 PM   #14
DIYBras is offline DIYBras  Brazil
diyAudio Member
 
DIYBras's Avatar
 
Join Date: May 2015
Location: Parana
This capacitor position seem to be strage at first glance, but it is a network "trick" (bootstrap) for making higher Z input. If you connect the capacitor like in your post, the input Z will be ~15k. In fact the stange connection is a positive feedback: in post #2, the open loop response has a huge peak at low frequencies, probably due a mismatch between capacitor values (is a side effect). In practice, my schema values makes a lot of motorboating, depending upon source Z input.

In fact, if low impedance is not a problem, I recommend to build one with your schematic modification. Will be far more stable.

Thanks for noticing this! So that I remembered this oscillation problem.
__________________
Making cabinets for OLD projects (better later than never...)
  Reply With Quote
Old 19th June 2017, 07:33 PM   #15
picowallspeaker is offline picowallspeaker  Italy
diyAudio Member
 
picowallspeaker's Avatar
 
Join Date: Apr 2007
Hi, I remember I built two amplifiers designed by Rockmandrake, you can search in the forum. I used them in my multi-amp with el. crossover experiments. High Zout was good for my woofer in open baffle ! ( I guess... )
__________________
Everything under and above heaven is in utter chaos
  Reply With Quote
Old 19th June 2017, 09:30 PM   #16
Ketje is offline Ketje  Belgium
diyAudio Member
 
Ketje's Avatar
 
Join Date: Dec 2012
Location: Flanders
Well leave the capacitor out all together.
Mona
  Reply With Quote
Old 20th June 2017, 04:06 PM   #17
stumpamp is offline stumpamp  Luxembourg
diyAudio Member
 
Join Date: Jun 2017
Quote:
Originally Posted by DIYBras View Post
I have other Ge amp but is a subject for another thread in future.
I am interested :-) Generally wondering about Ge Transistors, I just purchased like 10 different types via ebay. Built my first amp from those and it sounds like it got a waterfall inside.
  Reply With Quote
Old 26th June 2017, 03:44 PM   #18
DIYBras is offline DIYBras  Brazil
diyAudio Member
 
DIYBras's Avatar
 
Join Date: May 2015
Location: Parana
Quote:
Originally Posted by stumpamp View Post
I am interested :-) Generally wondering about Ge Transistors, I just purchased like 10 different types via ebay. Built my first amp from those and it sounds like it got a waterfall inside.
This Ge amp I mentioned is like old "booster" car amplifiers with inductors, but using the Susan Parker's Zeus amp discipline for making the transformers. It uses 9V supply
Have fun with Ge projects!
__________________
Making cabinets for OLD projects (better later than never...)
  Reply With Quote
Old 26th June 2017, 03:52 PM   #19
DIYBras is offline DIYBras  Brazil
diyAudio Member
 
DIYBras's Avatar
 
Join Date: May 2015
Location: Parana
Some transistor measurements
I have only 2 AD161, and my amplifier is a stereo one. So I use the 2. One of them have a too much downward beta, and have a suspicious high low current beta (like high leakage). Other have a fair beta variation but "stops" amplifying past 1.8A. Since the base network have low Z, even the high leakage AD works flawlessy here.
Four 2SB481 are measured. The two most linear are used in actual amplifier. They all have low beta, but at least a linear one. Since the "VAS" is a NPN and pull all current we want (limited by first stage), the PNP can be a low beta one and works OK.
A rusty spare AD162 is included for comparision.
The second graph is from 2SB481, and last graph is from 2SB486 (the low noise input)
Attached Images
File Type: png GeAD beta 1.png (27.7 KB, 45 views)
File Type: png 2SB481.png (21.3 KB, 44 views)
File Type: png 2SB486.png (19.0 KB, 42 views)
__________________
Making cabinets for OLD projects (better later than never...)
  Reply With Quote
Old 26th June 2017, 04:13 PM   #20
Osvaldo de Banfield is offline Osvaldo de Banfield  Argentina
diyAudio Member
 
Osvaldo de Banfield's Avatar
 
Join Date: Dec 2011
Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina
IMHO, capacitors on the schematic posted #4 are too big. Start (power on) times will be long, and pops and clicks when turning on or off, although audibly, they can destroy transistors.
__________________
Osvaldo F. Zappacosta. Electronic Engineer UTN FRA from 2001.
Argentine Ham Radio LW1DSE since 1987.
  Reply With Quote

Reply


A little study about two old germanium projectsHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Etude - Amplifier for study Patefon Tubes / Valves 4 9th August 2016 09:12 PM
New Amp on Study turnA_zpoint Solid State 0 7th March 2016 11:30 PM
Feasibility study 454Casull Multi-Way 10 22nd March 2009 01:23 AM
I want to study NoBit Digital Source 3 12th January 2008 03:35 PM
A study of current feedback digi01 Solid State 14 21st August 2006 01:01 AM


New To Site? Need Help?

All times are GMT. The time now is 05:56 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio
Wiki