Next project change. Another Hammond came my way.

[NO_H2O]

It has been a while since I have posted. But I have been here reading all the while.
I had been planning a SE EL34 combo but never really got that started.
But today I picked up an AO-35 with some extras. I have most of what is needed for the basic guitar conversion with a Marshall 18 watt single volume single tone pot and recap. It also came to me with the reverb tank (I think the tank will end up in my stash).
I still need to do the basic wire up so I can check all the voltages thru the amp before I move forward. But it has the original tubes and they do test good on my tester (I know that test only goes so far). And I look forward to hearing the Holland Amprex output tubes.
I only have one experience with an AO-35. I helped a friend get started with the basic conversion with a single 1 meg volume pot. It sounds great. Very Marshall like. But it goes into breakup very early. I know with the addition of a tone control some of that will be tamed. So I a hoping for good results and a more useful sweep on the volume control.
Any thoughts, tips or input would be great.

[TIMBO]

Hey mate, Used this tone stack, works well

Here is an idea for a chassis mod to make a control panel

If you can get a piece of flat sheet metal (1.6mm)the depth of the chassis and fold it to the length and enough at each end to fix it to the chassis, this will also shield the controls from the transformers.

[NO_H2O]

Great ideas. Thank you. I have a few pots and such. I will try that tone stack first. How is the sweep on the volume control with that setup?
I hooked this one up to my power supply and a speaker. Brought it up slow and took voltage readings.
All heater pins are 6.37 vac.

V1 pin1. 72.6
     Pin2.  0
     pin3. 0.57
     pin6. 150.9
     Pin7. 0
     Pin8. 1.56

V2 pin1. 251
     pin2. 18.8
     pin3. 20.8
     pin6. 202.5
     pin7. 14.5
     pin8. 0

V3 pin1. 0
     pin2. 0
     pin3. 21.5
     pin6. 0
     pin7. 257.5
     pin8. 0
     pin9. 237.2

V4 pin1. 0
     pin2. 22.2
     pin3. 21.6
     pin6. 0
     pin7. 248.5
     pin8. 0
     pin9. 238.1

I find the difference between V3 and V4 pin 2 readings odd. But the is no volume control so it is running wide open. There is some hum so a recap and better lead dress is in order. The heater wires are not well separated from the rest.

[DummyLoad]

looks like it led a charmed life - very clean inside and i'd bet the filters are fine. ground the tip of the phono cable and re-check for hum.


i'd put a 3 wire AC cord, rework just V1a and V1b to look like a deluxe 5E3 single channel or a hoffman stout. there's plenty of room in that chassis for a pair of controls and an input jack in front of the turret board. remove the barrier strips, move the output to the OT side of the chassis and fabricate a plate that covers the entire front. waste nothing but a few parts.


--pete

[sluckey]

I find the difference between V3 and V4 pin 2 readings odd.

V4-2 should be zero volts. Disconnect one end of C11. Does pin 2 now read zero? If so, replace C11.

Schematic attached...

Edit... Something to think about... The Dr. Z Carmen Ghia amp was converted from an AO-35.

[NO_H2O]

Thanks y'all. I will lift C11 in the morning and see what I get.

[NO_H2O]

I lifted one end of C11 and the voltage at pin 2 ov V4 is now 0. So I will add replacing C11 and C12 to my list of things to replace.
Thanks Sluckey.

[NO_H2O]

One more head scratcher. Shouldn't the voltage on V1 pin 1 be closer to V1 pin 6 for guitar use?

[drew]

Am I wrong or are these guys bolting AO-35s into tool boxes?  http://www.analogoutfitters.com/sarge/

[NO_H2O]

That's what it looks like.

[NO_H2O]

I have not made a lot of progress yet. I did get things cleaned up and got retainers on all the tube sockets. I still need to make a list, go thru all my stuff and see what I need to order from Doug.

[NO_H2O]

I think my first move will be to ditch C1, C3, R3, R5. I feel I need to raise the voltage at pin 1 on V1. Change R1A to 1M, change R1 something between 33K to 68K, change R2 to 1.5Kish and insert the tone/volume stack in place of R8.
If I am missing something. Just let me have it.
I have not sorted any changes from V1B on.

[sluckey]

I love converting these old Hammond. They're such a solid base and use quality parts. I've done several and still have two more AO-43s just waiting for some inspiration. I'll be following your project with great interest.

[NO_H2O]

I really enjoyed converting the AO-43 into the AC15. If I find another one at the right price, it will become a 6V6 Plexi.

[MFowler]

Here is some information I collected when I was building a Lite IIB from my AO-35 and talking to Mike Zaite I got some info plus he already had given much info on his forum.

[MFowler]

Notes I could not get in upper post.


Photo is my Lite IIB conversion and I ran with parallel V1.

[sluckey]

I really enjoyed converting the AO-43 into the AC15. If I find another one at the right price, it will become a 6V6 Plexi.

Would you consider $50 plus shipping a right price? Shipping from Mobile to Atlanta should not be too bad.

[NO_H2O]

I really enjoyed converting the AO-43 into the AC15. If I find another one at the right price, it will become a 6V6 Plexi.

Would you consider $50 plus shipping a right price? Shipping from Mobile to Atlanta should not be too bad.

Yes. That is a great price.

[NO_H2O]

Thanks for all the great info and ideas. Many great options to choose from.

[sluckey]

I've sent you a pm with some more info and links to a couple hi-rez pics of the AO-43.

[NO_H2O]

Thank you sir. I will take it off your hands. 

[NO_H2O]

Got a bit further along today. I cut down a door kick plate for some face plates. And drilled up the front and rear of the chassis to mount the needed devices. I used kleko's and still got one of my switch holes a bit off.
Now I must finish sorting thru my cap/resistor stash to see how far I can get. I did get the can caps swapped out.

[sluckey]

I love that amp cradle. I've used the same on every one of my Hammond conversions. Those chassis just beg for that type cradle. 

[NO_H2O]

It was quick and handy. A few screws and scrap plywood. I might build a nice one someday.

[NO_H2O]

Well last night I swapped out what I had wanted to do to V1. This morning I temp wired a speaker to the leads from the OT, plugged it into the variac and brought the power up slowly with only the 5Y3 plugged in and took voltage readings. I was almost done and as I was writing down voltages from V3 I heard a pop and lost B+ voltage. I shut it down and checked the secondary windings of the PT (all good). So I thought the 5Y3 died. I had a new JJ 5Y3 so I dug it out of the stash and plugged it in. B+ was back. So after a short pause to grieve the loss of the original Hammond 5Y3, I started over. Voltages with only the new 5Y3 were close to my original findings so I plugged in the remaining tubes. All the heater legs tested 6.48 vac. DC voltages are as follows.

V1
 Pin 1.  171
 Pin2.  0
 Pin3.  1
 Pin6.  164
 Pin7.  0
 Pin8.  1.1
 
V2
 Pin1.  236
 Pin2.  18
 Pin3.  20.5
 Pin6.  233.8
 Pin7.  17.3
 Pin8.  20.4

6BQ5's
V3
 Pin1.  0
 Pin2.  0
 Pin3.  10.5
 Pin6.  0
 Pin7.  297
 Pin8.  0
 Pin9.  287

V3
 Pin1.  1
 Pin2.  1
 Pin3.  10.5
 Pin6.  0
 Pin7.  293
 Pin8.  0
 Pin9.  286

It still has a good bit of hum and with the NFB leg disconnect it will squeal like a pig. My test speaker is an 8 inch 16 ohm unit.
Maybe the OT is to close to the tone stack. Or the heater wires are too close to the wiring from the board. I have replace the filter cap can. The insulation of the wire to the cap can melts very easy. And I could not get solder to flow to the chassis. Tried 2 irons, a 100 watt gun and a micro torch. Just don't have an iron with enough ass to do it so I ran a jumper wire to the ground lug I put in to ground the 3 prong power cable.
Here are some pix. If you see any faults, let me have it.

[NO_H2O]

I swapped out the output tubes with a pair of ri tung sol. No help. Still hums. I swapped V1 and 2 with some various 12AX7's I have and that was no help. But if I pull V1 and V2 it is quiet. So I must trace down the preamp section and find my problem. I also fabbed up an aluminum hood to shield the tone stack from the OT. That has no help as well. Back to work tomorrow so it will rest until next weekend.

[NO_H2O]

I did some poking around with a chopstick last night. Didn't find any suspect areas, or it didn't seem to make any change. Still have a constant 60 cycle hum. Changes in volume make a little change but not a great deal. Being 60 cycle hum I feel like it must be from the heaters or heater wiring. It was the same with 2 sets of tubes so I will try removing and replacing the circuit. I think I also raised the B+ on V1 a bit too much so I will knock that back down to the 120 to 130 range.
It would help if I post the schematic I am working from for round 1. I swapped in the standard 2 pot 18 watt Marshall stack in place of the stack shown.

[NO_H2O]

Has anyone had bad luck with CE cap cans? I got a replacement cap can with the amp and installed it. I'm Wondering if that may be the source of some of the hum I have. I don't have  cap test equipment so I think I would have to swap caps to test that. I have used one CE cap can and it worked well in my Vibro Champ.
I have some caps and wire coming from Doug and a fine Pace solder station on the way from Sluckey. I think I will wait for all to arrive before I jump back into this.

[NO_H2O]

The Pace solder/desolder station arrived from Sluckey today. I went to Home Depot and picked up an air pressure regulator to run a separate line over to my bench for the vacuum pedal. Set everything up and went to work at some lead dress of the heater wires. OMG. The vacuum function of the Pace station is awesome. I don't think I could ever go back to my old solder sucker. Plus the solder side is a great improvement over my old Weller station. Big thanks to Sluckey.
Anyway. I got the heater wires dressed out and down against the chassis and the others up and away from the heater wires. I replaced the 25uf @ 50 caps and will add 25uf cathode bypass caps to V1 tomorrow. I hope this will kill the hum I have.

[NO_H2O]

I got the heater wiring dressed and replaced C12 and C19 electrolitic caps yesterday. Today I re-flowed all the solder points, added 25uf cathode bypass caps on both sides of V1. And with fingers crossed I brought it up slowly again and the hum was gone. I then plugged it into my 4x12 cab, grabbed the old SG and gave it a quick try-out. This little amp has some bark. I need to have a real player put it thru its paces but so far I like it. It does seem to break up I bit early but I will have to see how it does with single coil pickups and someone that knows how to play.

[sluckey]

Maybe you and Ed could get together?

[NO_H2O]

That's a fine idea. I will have to look him up.

[NO_H2O]

I took the amp over to my sons house and he gave it a workout. It does break up too early so I think I will lift the cathode bypas caps that I added to both sides of V1 to try to cut the gain down. Also found that the volume pot will not completely kill the signal when turn all the way down. I also may swap the tone pot to a 250K as some of the sweep on the 500K tone pot is unaffective. But overall it is a winner.

[NO_H2O]

I lifted the cathode bypass caps from both sides of V1, swapped the tone pot from a 500K to a 250K and swapped out the 500K volume pot with another 500K. Gain is just right now. It starts breaking up at about 6 and is full on overdrive at 8. The tone sweep is still not full sweep and the volume pot will still not fully kill the signal. I will have to ring both of my 500K pots to see if they are bad pots. If not, I need to do some homework.

[sluckey]

Try directly grounding V1 pin 7 with a gator clip lead. Does that totally kill the signal?

[NO_H2O]

I will try that. It may have to wait a bit. I am having surgery tomorrow to fix a hernia and will be recovering for a few days. Getting old is not for wimps.

[NO_H2O]

Well I had to try it. I needed to go in and finish removing the cathode caps anyway. But no grounding pin 7 makes no difference. I also rang out the 500K pot that I removed with my meter and it checks ok. I re-flowed all the ground connection on the tone stack while I had the iron hot and that was no help. I think I have goofed it somewhere. I just need to map it out and find it.

[NO_H2O]

I found a roll of this off white tolex that my wife picked sometime back. I had the handle and some birch plywood so I thought I would build a head cabinet. I still need to flip the power and standby switches and flip the wiring on the tone pot as it operates backwards. But it sounds great.