Boggs here with my first post... and it may be a doozie...

[rp]

Welcome. I've destroyed stuff like this and I regret it, along with the all bugs I burned with a magnifying glass. Don't do it, eBay it to a hifi guy who'll love it as it is and use the money towards a new build. Maybe restore it first, trying to keep as many old parts, to up the value. Put a high enough reserve so someone doesn't just buy it and make a guitar amp out of it

[M Fowler]

I like the looks of that amp, should be perfect for a great tweed type guitar amp.

Mark

[boggs]

Welcome. I've destroyed stuff like this and I regret it, along with the all bugs I burned with a magnifying glass. Don't do it, eBay it to a hifi guy who'll love it as it is and use the money towards a new build. Maybe restore it first, trying to keep as many old parts, to up the value. Put a high enough reserve so someone doesn't just buy it and make a guitar amp out of it

If it were a stereo amp, I might agree with you more, but it is mono and I would prefer to see it actually used instead of sitting on a shelf somewhere alongside comic books that no longer get read... I will have the schematics to return it to original if ever... First thing I need to do is get new cans anyway 'cause it hums pretty badly.

[Phil_S]

I have a second pristeen chassis and front for it so I could essentially keep the original stock and get new sockets and such and start from scratch so to speak and just use the transformers...

Actually, you've got plenty to work with on the back face. You'll be removing the screw-terminal strip and replacing it with either a selector swtich and output jack or 3 output jacks. You might have to make a mounting plate for the inside or drill out the phenolic you've got. This is no big deal.

Then, you've got that oblong slot at the rear corner and there's nothing on the inside near it, so you can put just about anything there. I think this spot is opposite V1, so you've got a ready made spot for your input jack(s).

There is plenty of real estate inside. Lot's of possibilities.

BTW, I've checked eBait over the last couple of days. Maybe my eye for this particular type of amp isn't that sharp, but I'm thinking it would be worth more to me to keep it than to sell it. That was not my original thinkking, in case you are wondering what made me change my tune. If this were a Dynaco, Harmon Kardon, Fisher, etc, some of those sell for silly money and you could probably fund two projects with the proceeds.

[sliberty]

Actually, you've got plenty to work with on the back face. You'll be removing the screw-terminal strip and replacing it with either a selector swtich and output jack or 3 output jacks.

Then, you've got that oblong slot at the rear corner and there's nothing on the inside near it, so you can put just about anything there. I think this spot is opposite V1, so you've got a ready made spot for your input jack(s).

Everybody has their own style. Here is how I would handle it.

Leave the terminal strip in tact. Use it as your impendance selector, espectially since it is already connected to your output transformer. To the far right, there is a round hole - put an output jack there. Then, drill a small hole in the back of the chassis near the terminal strip to pull a wire through (use a grommet to protect the wire). This wire would go from the hot on the output jack to a banana plug. The ground would go to Common on the terminal strip of course. Then, I would use banana/spade connectors like in the eBay ad below on the screw terminals, and just plug the banana plug into the one I want (4,8,or 16).

http://cgi.ebay.com/16x-Adapter-Fisher- ... 41549f3736

I generally prefer to have the input jack on the front, even in a conversion like this, so I would locate it where the selector switch used to be.

See photos attached for examples.

Just another way to skin the cat.

Steve

[sliberty]

By the way - I have done conversions of two Heathkits before. They were EA2 and EA3 models as I recall. Very similar layout internally, and they came out sounding great. The iron is good quality for sure. Mine had a pair of EL84's, so I did AC15 circuits in them, one for my son, and the other for a customer.

[Phil_S]

I yield the the more experienced sliberty. I think, if I had the item on my bench, it is likely I'd have come to the same way of doing it. It is hard to do from pictures!

[rp]

I hate to see something so clean get mauled but it's hard to argue with the mono thing. Therefore, may I suggest a 5D4 tweed. You get to keep the layout, I wouldn't even move a single terminal strip. This also avoids any holes in the chassis. You can use 2 dual 20/20 FP cans

http://www.tubesandmore.com/ -> C-EC20-20-450

Best of all you get to keep all those nice old .047 caps if they're good. If you don't think they're nice old caps I'll take 'em!

I'd plan on 6L6s but I might try the 7591s first. You can always drop one channel and change the tone to bass and treble. Use a 5AR4 in case the 5V is only 2A. Use a fixed bias to keep the pot and anyone looking at it will think you're playing guitar through a stock Heath integrated amp.

Now that I think about it - have you tried playing guitar through it as is? Do the electrolytics first, test the voltages and the coupling caps for leakage. Might not need any mods, might be a cool discovery.

[boggs]

Lots to pick and choose from... Thanks so much, guys! I reallylike the banana plug idea on the output strip!

This is from the guy who sold me the amp on what he did with another one:

"Greg,

Here's a few versions of the circuit as I went through and tried various mods. I found a schematic online for the AA-181 that is identical to the AA-23 schematic in the builder's manual. I compared them point by point, they're the same. That was nice as I was able to edit the file and save the various versions. The last version (0 is very close to the circuit I ended up with for TCM. Just take the bypass caps from the tube cathodes and that's it.

You'll have to imagine the tubes rewired for 12AX7s though. I left the 6EU7 pinouts on the schematic as I meant it for my use when rebuilding your amp.

I put a post-phase inverter master volume in a friend's amp that doesn't show on these circuits. I didn't like it though and decided not to use it for myself. He wanted it.

The final preamp tube set I ended up with on the other guy's amp was V1=12AX7, V2=12DW7, V3=12AU7. Man, that setup sounded sweet!

http://www.visi.com/~sstolle/Heathkit.zip

Hope this helps. Feel free to ask any questions. The original circuit for this amp is not unlike some early Ampeg amps and that was the tonal vibe I was going for. I think it hit pretty close to the mark."

Thoughts?

Boggs

[Baxtercat]

Welcome. I've destroyed stuff like this and I regret it, along with the all bugs I burned with a magnifying glass.

Too funny....describes me too.
For all my guilty reminisces regarding dead bugs, refinned Strats, rewired chasses, I still got excited when I saw the pic of your Heathkit.
"Ooo, let's fiddle with it." Yet we're lucky it sounds as good as a Blues Jr. when finished.

[rp]

Welcome. I've destroyed stuff like this and I regret it, along with the all bugs I burned with a magnifying glass.

Too funny....describes me too.
For all my guilty reminisces regarding dead bugs, refinned Strats, rewired chasses, I still got excited when I saw the pic of your Heathkit.
"Ooo, let's fiddle with it." Yet we're lucky it sounds as good as a Blues Jr. when finished.

The guilt I carry forever, but is there a Statue of Limitations? I think the Mounties are still after me for all the Traynors I butchered.

-rp

[gldtp99]

I like the looks of that amp, should be perfect for a great tweed type guitar amp.

Mark

I agree---- i'd drop the 7591's and use 6L6GC's--- but that's because i have a good stash of old production 6L6-types and no 7591's. 6eu7's sound great, just like 12ax7's--if this amp were mine i might keep the 6eu7's because i have a stash of quality replacements. If you don't, then 12a_7's may be the best way to go because of easier/cheaper access.
Three 9 pin preamp sockets, two output tubes, and a 5ar4---many possibilities here.................gldtp99

PS--- FWIW---- just because some certain guitar amp circuit is "known" for a particular tone structure, in stock form, it doesn't mean that you have to build the circuit exactly like any schematic---it's your amp, build it to your needs.
For example: i got a beat-up, modded, oscillating, 1976 Marshall model 1987 (50 watt head) a few yrs ago----i went through it and re-configured it for much later onset of distortion than these amps are commonly known for----- a blues purist (Fenders forever, sometimes an old Ampeg) friend played it and was amazed at what rich clean tones this circuit is able to produce, at band-level vols, with a few changes. It will still produce great distorted tones but it needs to be played extremely loud to do so--- no problem, i have other amps for lo vol distorted tones.
I think you'll learn a lot from this project...................gldtp99

[boggs]

What would you all suggest for an easy to absorb and comprehend publication to help me actually LEARN something about the hows and whys of tube guitar amp circuitry particularly with respect to taking on this project?

[Bob-I]

What would you all suggest for an easy to absorb and comprehend publication to help me actually LEARN something about the hows and whys of tube guitar amp circuitry particularly with respect to taking on this project?

http://ax84.com/p1/P1_Theory_Document.zip

Read this, once you understand the sections of the amp you'll also need to understand a push pull amp, there's some info on phase inverters on http://www.aikenamps.com

[Phil_S]

What would you all suggest for an easy to absorb and comprehend publication to help me actually LEARN something about the hows and whys of tube guitar amp circuitry particularly with respect to taking on this project?

Merlin Blencowe quite literally wrote the book, "Designing Tube Preamps for Guitar and Bass." It's ironic, that a Brit called it "Tube" or else he publishes as "Valve" in the UK.