How to convert Hammond AO-39 pwr amp to accept SS guitar preamp?

[smackoj]

I have been trying to build my own 'hybrid' guitar amp off and on for many months. I had good success with mating a vintage SS organ amp to my Peavey Renown 'Pre Amp Out' jack and it worked exceptional with almost no mods. But I am now wanting to experiment with a tube output section instead of SS. I purchased a Hammond AO-39 chassis complete off Sneezbay and it already has a tube layout that should allow a PI, two EL84 pwr tubes and a rectifier tube. I looked on the web and immediately found SLuckey's great post (with pics) on how he converted the AO39 to a Vox AC15 Lite amp. He also generously included how to convert the 39 to the Marshall 18 Lite II.

Could one of you fine gents give me a nudge in the right direction to mod the input side of the AO39 to accept a 'line in' from the Peavey SS preamp 'line out' ?  thanks much

[eleventeen]

I see no reason why it shouldn't at least partially work just as it is.


What I would do is for a first shot, where the dwg says "signal in" get your (I assume Hi-Z) line signal (hot, gnd) to the red & black and ignore chassis ground for the tube amp. That might work, it might produce a bad hum issue. If you look at the two halves of the input 12AX7, they are identical, and they apparently have sufficient gain to take 260 mv (1/4 volt = Strat p/u output) and drive your 6BQ5 output tubes. Thus the balanced signal wants to be about 1/2 volt, which is in the ballpark of a typical line out. Perhaps you will need a pot to lower the preamp drive signal. It looks like the input stage wants in effect a balanced signal. (Two hots and a ground)


Anyway, perhaps you'll have a slight/clumsy/unworkable level mismatch. I don't think you'll blow anything up and maybe you'll be pretty close to what you want just as it is.


I would try that before tearing the thing apart. It's a 6BQ5 powered amp exactly as it is.

[sluckey]

give me a nudge in the right direction to mod the input side of the AO39 to accept a 'line in' from the Peavey SS preamp 'line out'

That's exactly what I did when I first started playing with the AO-39. You cannot use the V1 circuit as is The AO-39 has a dual driver (V1) as an input. IOW, the phase inverter is on another chassis. So, just convert V1 dual driver circuit to a LTP PI circuit. Use this schematic...

     http://home.comcast.net/~seluckey/amps/hammond/hammond_ao39.pdf

...and use this hi rez pic to see how I modified the V1 circuit...

     http://home.comcast.net/~seluckey/amps/hammond/AO39_conversion.JPG

[smackoj]

should I use the 500KA vol. pot before the PI or just straight in to the .01 uf capacitor?  thanks mucho.

jack   

[Skip Hagey]

" So, just convert V1 dual driver circuit to a LTP PI circuit. "

I'd like to jump in here and ask SLuckey if the preamp stage is still on "another board" and your just coming to the LTPI from the input jack?  Very cool if so, cause it looks like very little to do except make a suitable preamp and Bob's your Uncle....

[sluckey]

should I use the 500KA vol. pot before the PI or just straight in to the .01 uf capacitor?  thanks mucho.

You can do that if you want to be able to control the signal level coming from the preamp. Otherwise, just connect the input jack straight to the cap like I did in the pic.

This was just a test circuit so I could find out how the AO-39 sounded with some different preamps. I have a preamp out jack on several of my amps so it was an easy way to tell. The AO-39 is a nice sounding power amp just as it is.

[sluckey]

I'd like to jump in here and ask SLuckey if the preamp stage is still on "another board" and your just coming to the LTPI from the input jack?

That's correct. I forget which organ the AO-39 was used in but the preamp was on a different chassis. That chassis also had an interstage transformer that acted as a phase inverter to produce the two out of phase drive signals for the output tubes on the AO-39 chassis.

[smackoj]

muchas gracias senor Sluckey.

 

[tremelo68]

     http://home.comcast.net/~seluckey/amps/hammond/hammond_ao39.pdf

...and use this hi rez pic to see how I modified the V1 circuit...

     http://home.comcast.net/~seluckey/amps/hammond/AO39_conversion.JPG

Hy sluckey,I can't seem to get to your pages. Do you still have this info online?

[sluckey]

Sorry. Comcrap has decided to no longer support personal websites. They shut the FTP server down last week which meant I could no longer update anything. Looks like today they finally removed all files. I have not figured out what to do about it.

[DummyLoad]

Sorry. Comcrap has decided to no longer support personal websites. They shut the FTP server down last week which meant I could no longer update anything. Looks like today they finally removed all files. I have not figured out what to do about it.

dropbox. at least for the file sharing.

we bought comcast 10gig ethernet circuit service to connect 2 data centers. we kept if for just over 1 year. it's the only service we have disconnected in over 20 years before contract term end because of reliability, long outages, and severe packet loss. it cost us money to buyout the remaining contract term. it was worth it.

costs you money but...

Godaddy

i doubt a buk a month will break the bank.    considering it myself.
 
--pete

[sluckey]

Go Daddy does look interesting. Intro price sounds good. I'm just not sure why I would want to bother putting all that stuff back online. Having my stuff on display meant a lot more to me at one time than it does today. I'll just hang lose for awhile and see how I really feel about it. I'd be interested to hear about your experience with Go Daddy if you decide to sign up with them.
 

[PRR]

> i doubt a buk a month will break the bank.

Interesting sucker-bait. You don't get that deal unless you get a domain name. Which for 90+% of customers will revert to GoDaddy when you quit. The cost without domain is 4X higher. So GoDaddy is collecting domains, willing to forego a few bucks to do so.

GoDaddy is the gorilla of small sites. IIRC, our host Doug tried them, found they lacked specific script support, and were totally un-sorry about that. He cancelled-out in a few days and went with somebody else. Of course the needs of a complex and custom coded shopping site with high-traffic forum are different from ordinary folks.

[DummyLoad]

Go Daddy does look interesting. Intro price sounds good. I'm just not sure why I would want to bother putting all that stuff back online. Having my stuff on display meant a lot more to me at one time than it does today. I'll just hang lose for awhile and see how I really feel about it. I'd be interested to hear about your experience with Go Daddy if you decide to sign up with them.

will do.


--pete

[TIMBO]

This was a basic SS preamp into a tube output http://www.guitargear.net.au/discussion/index.php?topic=45138.0