Resurrection: Old Parts - New Amp. - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 7th February 2009, 12:14 AM   #1
Account disabled at member's request
 
MJL21193's Avatar
 
Join Date: Mar 2007
Default Resurrection: Old Parts - New Amp.

I don't need any more amps.

BUT...

I have these parts that are bothering me - mocking me, daring me to use them. They were once in the thick of things, members in casts of hundreds brought together to reproduce music. Their implementation was less than ideal, somewhat undeserving of their (near) excellence.
I liberated them from the bonds of mediocrity, ill repair and flat-line status to one day be used in a project that could be a more deserving purpose. Could be a new beginning... a revival from the dead.

Here are some:

Click the image to open in full size.

Old solders, scarred and rough. We see sergeant Toshiba, lieutenant Panasonic, colonel Sanken and marshal NEC. Also in attendance is corporal Mitsubishi. All battle hardened veterans, but with many years of service left to offer.

I have some ideas, some plans to try and make the best of these. Putting them into modern uniforms with new support troops, playing out a modern war on a bright new battlefield.


I'm working with a schematic that I'll post shortly.
  Reply With Quote
Old 7th February 2009, 02:13 PM   #2
Account disabled at member's request
 
MJL21193's Avatar
 
Join Date: Mar 2007
Heatsink and transformer:

Click the image to open in full size.

The heatsink is from an old Pioneer and the transformer came out of either an 80's era Fisher or a Kenwood, i can't recall. It's a 40-0-40, probably 300VA or better.

I'm still working up a schematic but have had some distractions. I want to use the 2SA798/C2291 for a symmetrical complementary differential input stage. These are monolithic pairs with 5 pins (emitter is common). 50V, so I'm looking at a cascode on each to work at the higher voltage.

A look at the proposed front end. Suggestions?
Attached Images
File Type: png 114.png (17.3 KB, 1395 views)
  Reply With Quote
Old 7th February 2009, 11:41 PM   #3
Account disabled at member's request
 
MJL21193's Avatar
 
Join Date: Mar 2007
Wow, not much interest...

It only looks like a pile of junk
These parts cost me next to nothing - most are out of old non functioning amps and receivers that I picked up cheap or had given to me for nothing. The objective is to build a high quality 2 channel amp from these parts, without using anything new (except electrolytic caps and resistors).

Full schematic below. The input pairs are the monolithic 2SA798/c2291 and for the cascode and CCS I will use original NEC 2SC1845/A992. I have plenty of the C1845 but I'm short 1 A992. I'll need to do a bit more looking.

For the VAS, I've picked the 2SA949 and the 2SC2229. These are fast, low Cob and high enough voltage for the task. They are running at ~2mA, so dissipation will not be high.
Attached Images
File Type: png 114.png (44.2 KB, 1377 views)
  Reply With Quote
Old 8th February 2009, 12:18 AM   #4
SQLGuy is offline SQLGuy  United States
diyAudio Member
 
Join Date: Jan 2009
Looks like a fun project.

In the amp I'm working on now, though, I think I am dealing with some transistors that test fine and still amplify, but are damaged and causing annoying levels of noise.

I would be concerned the some of the pulls you have among your parts may be similarly damaged. Do you have enough extras to swap parts in and out to get a "good" set, or do you have a good way to test them more comprehensively?
  Reply With Quote
Old 8th February 2009, 12:58 AM   #5
diyAudio Member
 
ostripper's Avatar
 
Join Date: May 2008
Location: Smoky Mountains , Tennessee
Quote:
It only looks like a pile of junk
Glad to see somebody is helping to clean the planet besides me.

I am ADDICTED to junk , have all the kids bring it to me for
extra candy money/cell phone minutes. Trannies are suspect
unless unit is newer and had just low voltage issues.

If newer, Caps and trafo's are gold ($$$$) , more money for
better caps and LM4702's.. which by the way ,are great for
using your typical HT reciever "guts" (darlington or big sanken)
here is my latest find// $1.00 for "candy"..

BTW ..zener and decouple your cascodes ...15v zener to ground
and 10u to rails...

OS
Attached Images
File Type: jpg stripped.jpg (23.9 KB, 1351 views)
  Reply With Quote
Old 8th February 2009, 01:58 AM   #6
Account disabled at member's request
 
MJL21193's Avatar
 
Join Date: Mar 2007
Quote:
Originally posted by SQLGuy
Looks like a fun project.

In the amp I'm working on now, though, I think I am dealing with some transistors that test fine and still amplify, but are damaged and causing annoying levels of noise.

I would be concerned the some of the pulls you have among your parts may be similarly damaged. Do you have enough extras to swap parts in and out to get a "good" set, or do you have a good way to test them more comprehensively?

Hi SQLGuy,
I have quantities of several with a few exceptions: The NEC outputs are fairly rare and I haven't found any others. I do know these are working well though as they were pulled from an amp that was working fine. I already noted the 2SA992's, and that I'm one short (need 8 in total). I have since found 5 more, so I have some spares. These I have tested with my DMM just to get an idea if they are viable. I could create a "testbed" to run these transistors on, but I think I'll roll the dice and try them in the final circuit. If there is a problem, It should be easy enough to spot.

More device talk: I chose the 2SC2590 and the 2SA1110 for the CFP "slave" stage and the 2SA1490/2SC3854 Sankens (no spec sheet links available) as the drivers. I have these running hot and contributing to the output.
  Reply With Quote
Old 8th February 2009, 02:15 AM   #7
Account disabled at member's request
 
MJL21193's Avatar
 
Join Date: Mar 2007
Quote:
Originally posted by ostripper


Glad to see somebody is helping to clean the planet besides me.

BTW ..zener and decouple your cascodes ...15v zener to ground
and 10u to rails...

OS

Hi OS,
I think it's something that more should do here (rather than endlessly chat, dream, argue and pose) - you can easily strip enough out of a receiver or two to build a very good amp for next to nothing. I have excellent new parts that I could use to build with, but this will be a nice challenge and a way to justify my childhood tendency to take everything apart...

You are forgetting that I don't like the evil zeners in that position. A voltage divider like I have used for Patchwork works very well.
I did fail to put a decoupling cap on my voltage divider to ground though, and thanks for reminding me. I will use a 1uF MKP or ceramic.
Speaking of which, why are we using silver mica for Cdom when a good quality ceramic will do the job? Is there really that much of a difference?
  Reply With Quote
Old 8th February 2009, 02:42 AM   #8
diyAudio Member
 
ostripper's Avatar
 
Join Date: May 2008
Location: Smoky Mountains , Tennessee
Quote:
why are we using silver mica for Cdom when a good quality ceramic will do the job? Is there really that much of a difference
Here is what I found out , it is not the material of the cap that
is the issue , it is the construction that matters. multiple layer ceramics are the same as silver mica's , just cheaper..

The single 2 plate ceramics sometimes exhibit resonance
at certain frequencies (just like 2 parallel PCB traces).
Miller compensation is a resonate circuit , so adding another
pole might not be good.



Quote:
You are forgetting that I don't like the evil zeners in that position
Then use some precision Vreg IC's (dirt cheap) ,or even 78/9 -15's (scrap)..
OS
  Reply With Quote
Old 8th February 2009, 03:15 AM   #9
Account disabled at member's request
 
MJL21193's Avatar
 
Join Date: Mar 2007
Quote:
Originally posted by ostripper

multiple layer ceramics are the same as silver mica's , just cheaper..

Then use some precision Vreg IC's (dirt cheap) ,or even 78/9 -15's (scrap)..
OS

I made a mistake on a Digikey order last year and got 100pF ceramics instead of 100nF bypass caps. I ran out of silver mica to finish my six channel amp and tried the ceramics - they worked fine, no problems. Sounds the same to me too(that doesn't mean much).
I up for trying it here also.

Why do you think I need to complicate the cascode supply? The voltage regulators you mention will not operate (for long) at my supply voltage.
My voltage divider gives ~28VDC for the cascode at 1.2mA - very good and simple.
  Reply With Quote
Old 8th February 2009, 03:42 AM   #10
jaycee is offline jaycee  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Norwich, UK
Also the ceramic dielectric must be the high stability type. A lot of them vary capacitance widely with voltage and temperature.

The only thing that would give me the willies about using parts like this, is what happens if they break? OK, in the case of the transistors, you could sub modern parts. I have some nice 2SK389 dual FET's from the Teac amp I gutted, but am cautious about using them because they are pretty much irreplaceable.
  Reply With Quote

Reply


Hide 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
The Citation 16A resurrection project taj Solid State 19 18th June 2007 04:54 AM
Half-dead Rotel RB-850 resurrection Mguth Solid State 13 29th December 2006 12:08 AM
PARTS PARTS PARTS!!! Infocus Powerview 820, triplet, ballast, light, power supply!!! marioinla Swap Meet 1 31st August 2004 05:22 PM
Comparison of SMD parts to standard parts BrianGT Parts 0 2nd July 2002 10:09 PM


New To Site? Need Help?

All times are GMT. The time now is 11:37 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2