I finally was able to pick up an amp to work with. This is what I've been wanting to do...Modify, Improve, and Learn as I go. I was hoping to get some help and opinions here and also share my experience with all.
The amp I have is a Harman Kardon A500, discribition ans Schematics can be found at this link.
http://intra.engr.uark.edu/~lar/fireamps.html
Please I am in the learning stage any help or suggestions would be greatly appreciated. No matter how small or trivial you may think it to be, I am in the learning stage.
Thanks Steve
The amp I have is a Harman Kardon A500, discribition ans Schematics can be found at this link.
http://intra.engr.uark.edu/~lar/fireamps.html
Please I am in the learning stage any help or suggestions would be greatly appreciated. No matter how small or trivial you may think it to be, I am in the learning stage.
Thanks Steve
Mods
Congrats on the vinatge amp. If I owned the amp, I would replace the electrolytics in the power supply. Next, I would change the coupling caps to AuriCap.
Next, I would build a socket adapter to change the 12AU7 to a Sylvania 6SN7GT with the 'T' type plates. Sylvania makes a short glass version that will fit under most cabinet covers. I have not ever found a 12AU7 I like sonically. Finally, I would try some various manufacture 12AX7s to tune the sonics.
Congrats on the vinatge amp. If I owned the amp, I would replace the electrolytics in the power supply. Next, I would change the coupling caps to AuriCap.
Next, I would build a socket adapter to change the 12AU7 to a Sylvania 6SN7GT with the 'T' type plates. Sylvania makes a short glass version that will fit under most cabinet covers. I have not ever found a 12AU7 I like sonically. Finally, I would try some various manufacture 12AX7s to tune the sonics.
Before changing 12AU7 to 6SN7
Any restoration of a vintage tube amp should start with replacement of the electrolytic capacitors as suggested. That means Power Supply Caps AND any Cathode bypass etc. electrolytics.
If you can find someone in your area with a tube tester its a good idea to run all the tubes through the tester. Any tube which tests below 70% of published data sheet gm gets replaced.
I'll probably run into howls of indignation here BUT I do not like Auricaps. I've tried them in 3 different amps and in each case I thought they severly limited the high frequency response. Please, any other DIY'ers with experience of Auricaps vs other good Polypropylene Caps don't let me lead this fellow astray if you disagree.
Before trying the 12AU7 to 6SN7 change which requires some rewiring I would try a modern production JJ Tesla ECC99 in the 12AU7 socket. No rewiring needed and they seriously give 6SN7s "a run for their money".
Cheers,
Ian
Any restoration of a vintage tube amp should start with replacement of the electrolytic capacitors as suggested. That means Power Supply Caps AND any Cathode bypass etc. electrolytics.
If you can find someone in your area with a tube tester its a good idea to run all the tubes through the tester. Any tube which tests below 70% of published data sheet gm gets replaced.
I'll probably run into howls of indignation here BUT I do not like Auricaps. I've tried them in 3 different amps and in each case I thought they severly limited the high frequency response. Please, any other DIY'ers with experience of Auricaps vs other good Polypropylene Caps don't let me lead this fellow astray if you disagree.
Before trying the 12AU7 to 6SN7 change which requires some rewiring I would try a modern production JJ Tesla ECC99 in the 12AU7 socket. No rewiring needed and they seriously give 6SN7s "a run for their money".
Cheers,
Ian
I have the A300. Very nice little amp that uses 6V6s for outputs, otherwise very similar. I agree that the electrolitics should be changed, tubes tested and weak or shorted ones replaced, but then give it a listen. If you want to start making changes then at least you know where you started from.
New coupling caps, new resistors, different circuit configurations can all be tried. I'm just saying give the stock amp a chance before you start modifing. Get to know it before you make changes so you can better judge what the changes do to the sound.
Later
BZ
New coupling caps, new resistors, different circuit configurations can all be tried. I'm just saying give the stock amp a chance before you start modifing. Get to know it before you make changes so you can better judge what the changes do to the sound.
Later
BZ
AuriCaps- severly high freq limited
Out of five different amps, I never had that AuriCap issue. On the Scan Speaks & Seas Excel speakers, the high frequencies are bright and ultra clear. A stick hit on a rim or brush on a cimbal is accurate and easy to hear. No siblance on female voices either.
I also find AuriCap without midrange smearing unlike other caps I tested in its price range. My present amps are DIY PPP 6B4G & DIY PPP triode connected 6V6GT monoblocks with an Amperex 7308 phase splitter (no input tube required). Both are very accurate amps.
Out of five different amps, I never had that AuriCap issue. On the Scan Speaks & Seas Excel speakers, the high frequencies are bright and ultra clear. A stick hit on a rim or brush on a cimbal is accurate and easy to hear. No siblance on female voices either.
I also find AuriCap without midrange smearing unlike other caps I tested in its price range. My present amps are DIY PPP 6B4G & DIY PPP triode connected 6V6GT monoblocks with an Amperex 7308 phase splitter (no input tube required). Both are very accurate amps.
Now ya see I like he old point to point wiring stuff. Printed circuit boards were invented for manufactureabilty (is that a word?) and lower cost (read cheaper labor), it took some skill to do point to point. Those who try for the shortest signal path use point to point.
In the tube era a correctly done point ot point wiring job was more reliable than a circuit board. The heat from the tubes could damage the circuit board and cause intermittent problems and there are more solder connections with a PC board.
It's all in what you are used to.
Later
BZ
In the tube era a correctly done point ot point wiring job was more reliable than a circuit board. The heat from the tubes could damage the circuit board and cause intermittent problems and there are more solder connections with a PC board.
It's all in what you are used to.
Later
BZ
HDTVman said:
I certainly wasn't lamenting the lack of a PCB. I wire all my amps p2p.
There's a lot of complexity inside this integrated amp with the phono stage and the tone circuits, etc. The wiring is all over the place. It looks more like a bird's nest than an amp. A novice poking around in there with fingers or a soldering iron might break something and have a hard time fixing it.
When I first got the A300, I was a novice and I thought of modifying it. I opened it up, took one look, put the cover back on and went on to the next idea. Maybe I shouldn't have been daunted, but building a simple SET kit looked far easier to me at the time.
Well when I started out that amp wasn't that old. Point ot point was the norm and circuit boards were the "new thing".
I just learned on that old stuff so its easy for me to follow because functions are grouped in areas.
I agree that the volume control, balance control, tone control and filters can be tough to follow, but I don't think the rest is so bad.
Later
BZ
I just learned on that old stuff so its easy for me to follow because functions are grouped in areas.
I agree that the volume control, balance control, tone control and filters can be tough to follow, but I don't think the rest is so bad.
Later
BZ
Thanks this is all great info that I plan to follow. My intentions are hands on experience learning. My goal is not so much to restore this amp as to learn as I go. So if you follow my link to the Schematics can anyone tell me the Power and OPT are large enough to switch the tubes, redesign....I'm open to anything. This is my first so I don't want to be boxed in to just restoring but I want to learn what I have and what I do with it and eventially knowing enough to design my own or knowing how and why to tweak.
http://intra.engr.uark.edu/~lar/fireamps.html
Thanks again for all the input
Steve
http://intra.engr.uark.edu/~lar/fireamps.html
Thanks again for all the input
Steve
I am assuming by lack of response this particular amp (h/k A-500)
is suitable for nothing other than restoring with no real modifications. If this is true I guess I will just have to restore (Replace) componets...Caps resisters and things like this. I guess there is some learning to that. I was really hoping I came up with an amp that I could learn what happens when I change out this or how to sub different valves. I'll just have to come up with something else to modify and learn.
Thanks Steve
is suitable for nothing other than restoring with no real modifications. If this is true I guess I will just have to restore (Replace) componets...Caps resisters and things like this. I guess there is some learning to that. I was really hoping I came up with an amp that I could learn what happens when I change out this or how to sub different valves. I'll just have to come up with something else to modify and learn.
Thanks Steve
Have you read this sticky thread and some of the links referenced?
http://www.diyaudio.com/forums/showthread.php?s=&threadid=38278
Once you understand some of this stuff, ideas about what to do will pop into your head.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=38278
Once you understand some of this stuff, ideas about what to do will pop into your head.
Remember also that that amp uses 7355 outputs ... these are by no means common.
Also, by the time the signal makes it through all those pots, switch contacts and the two PEC's, I doubt that there is much of a difference between mid-range and 'boutique' components.
I also would not start by enlarging the chassis for octal tubes, etc. IIRC, the kit-assembly manual does not specify current capacity of the transformer winding. And besides, the topology will limit the perception of a components 'goodness'. One of the great things about parafeed SET amps is that changing almost anything changes the sound. More complex components tend to not share this virtue (just my opinion).
You're already going to have 'fun' with the power supply caps - if you want to preserve the original look (which is quite cool), you're going to have put new caps in the old cans.
If you need a part, let me know. I have most of the parts of an un-assembled kit.
If it was me, I'd be thinking Vishay/Dale 1/2 watt resistors for anything 1/2 or 1/4 watt, and Panasonic polypropelene and electrolytic capss. Available from Digi-Key for the caps, and Mouser for the resistors.
Have fun.
Also, by the time the signal makes it through all those pots, switch contacts and the two PEC's, I doubt that there is much of a difference between mid-range and 'boutique' components.
I also would not start by enlarging the chassis for octal tubes, etc. IIRC, the kit-assembly manual does not specify current capacity of the transformer winding. And besides, the topology will limit the perception of a components 'goodness'. One of the great things about parafeed SET amps is that changing almost anything changes the sound. More complex components tend to not share this virtue (just my opinion).
You're already going to have 'fun' with the power supply caps - if you want to preserve the original look (which is quite cool), you're going to have put new caps in the old cans.
If you need a part, let me know. I have most of the parts of an un-assembled kit.
If it was me, I'd be thinking Vishay/Dale 1/2 watt resistors for anything 1/2 or 1/4 watt, and Panasonic polypropelene and electrolytic capss. Available from Digi-Key for the caps, and Mouser for the resistors.
Have fun.
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