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:
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.
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:
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.
Heatsink and transformer:
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?
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?
Attachments
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.
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.
Attachments
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?
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?
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 forbetter 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
Attachments
SQLGuy said:
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.
ostripper said:
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?
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.
Then use some precision Vreg IC's (dirt cheap) ,or even 78/9 -15's (scrap)..
OS
ostripper said:
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.
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.
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.
jaycee said:
Tennyson said it best: "Better to have loved and lost than never to have loved at all"
I say use 'em, and if they break, are you any worse off? They are only valuable if you put them to good use.
As for the ceramics, the 100pF I have are 500V AVX and I couldn't see a difference during testing. Some (many) have prejudices against certain type of caps and ceramic is no exception. I would like to know if there is a truly valid reason for this bias. I have yet to open an older receiver or amp that has a silver mica anywhere to be seen. Granted, none of the amps I scrap are "audiophile" quality.
That's nearly £17 in my currency, and undoubtedly i'd have to pay extra on top of that for shipping and tax. And what would I do with the surplus parts?
I'll keep them for something like a headphone amp. If they go in that, i'd be more prepared to build a new circuit than i would be prepared to rebuild a 100W/8 ohms power amp.
I'll keep them for something like a headphone amp. If they go in that, i'd be more prepared to build a new circuit than i would be prepared to rebuild a 100W/8 ohms power amp.
ostripper said:
The transformers and heatsinks, case if you can recycle it. Transistors, film caps (tons), rectifier diodes, screws, fuse holders, pots, knobs and hardware, etc. I draw the line at resistors (too much work to measure and sort each) and electrolytic, especially the PS ones. Life span and unknown abuse are factors. I had an Akia that had one that was swollen and the other had ruptured. Some things are not worth saving.
jaycee said:
Sell them to someone here. I wouldn't want them though...my ears are not golden enough for such refinements. Low noise bjt inputs are as good as it needs to be for me.
New schematic. I have added decoupling to the cascode to ground and tidied it up a bit.
The Vbe multiplier will use the 2SC4137 which I found in a Kenwood receiver. These are supposed to be for temperature compensation and have incredibly high gain. I'm not sure if I have the Vbe multiplier configured properly for there use. I guess I will need to try it and see.
Attachments
I use to regularly visit my local recycling centre although I haven't been in a year or more. Great source for parts although they don't like you taking things away - in fact openly object to it. Seeing as you have to pay €15 to drop anything off I reckon you should also be allowed to pick up anything you might find useful - I see the staff do it themselves.
Anyway, some goodies I retrieved include
- a Rogers Cadet III tube amplifier- fully working with 4 ECL86 tubes & 3 ECC807 tubes (worth about €100 on ebay) - I've since rebuilt it into a Baby Huey amp using the PS & o/p trafos & tubes
- 3 Samson servo 550 studio amplifiers 275W per channel - all working except for one - good source for large heatsinks, case, 55-0-55 trafo ( I've used one of these as a voltage converter for US gear - gives balanced power), 6 SA1943 & 6 SC5200 + driver transistors in each amp - I'm building a Krill O/p stage with these
- Rega planar II turntable with glass platter - needs a belt.
All of these were found in good shape mainly because I was lucky & lots of other junk hadn't been thrown in on top of them. It breaks my heart to think of all the good stuff that has gone to be broken down in the year I've been away.
When I retire I want a job there!
Anyway, some goodies I retrieved include
- a Rogers Cadet III tube amplifier- fully working with 4 ECL86 tubes & 3 ECC807 tubes (worth about €100 on ebay) - I've since rebuilt it into a Baby Huey amp using the PS & o/p trafos & tubes
- 3 Samson servo 550 studio amplifiers 275W per channel - all working except for one - good source for large heatsinks, case, 55-0-55 trafo ( I've used one of these as a voltage converter for US gear - gives balanced power), 6 SA1943 & 6 SC5200 + driver transistors in each amp - I'm building a Krill O/p stage with these
- Rega planar II turntable with glass platter - needs a belt.
All of these were found in good shape mainly because I was lucky & lots of other junk hadn't been thrown in on top of them. It breaks my heart to think of all the good stuff that has gone to be broken down in the year I've been away.
When I retire I want a job there!
jkeny said:
Excellent finds! I leave the tube stuff where I find it though.
I hit the garage sales (occasionally) in the summer and Goodwill, Sally Ann. "Antique" shops/used furniture though these are expensive - no fun unless it cost nothing or next to it.
The garage sales are really good for vinyl - I found a giant stack last year, asked the lady how much for the lot. $5.00 for almost 100 records in near perfect shape.
I have the schematic where I want it (assume it's ok, no comments from the audience) and I've started the layout. The heatsink (pictured above) has a angle on the bottom, a place for the outputs to mount vertically with the sink standing up and a place on the bottom of the angle to fasten the sink (and PCB) to the chassis. Both channels are on this heatsink so I need to make a fairly narrow layout.
BTW, amps will be ~60 watts per channel, over voltage is for clipping headroom.
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