Hoffman AB763 Trem-O-Nator Upgrade

[purpletele]

Symptoms keep changing

If you're bored can you recap, I'm at low notes distort, not sure what high notes do?

thanks

Once I put everything back together with the shielded wires I started getting a little more distortion throughout.   

The EADG strings are really affected more than the B and high E.  The D string, if I slide from G to A it sounds like bacon frying.

Also, unless I'm hearing things, the scaping and scrubbing that I did in that area seemed to help.

Is this where an O Scope becomes really useful?

I think I will film it and post a video.

[shooter]

sounds like bacon frying.

typically; arcing, bad solder
you should be able to inject a "pick your note" and make bacon sounds with a stick
take your time.

Is this where an O Scope becomes really useful?

not quite, but I'd be saving up 

[purpletele]

Here is a link to a quick video I did to identify the Tremolo performance and a quick highlight of the distortion

[sluckey]

Have you checked the output tube bias since you did this mod?

[purpletele]

Have you checked the output tube bias since you did this mod?

I'll check that here shortly, that's a good point.  I'll also reflow some of the joints that I changed.

[purpletele]

Have you checked the output tube bias since you did this mod?

I had the bias a little low, I have JJ 6l6 GC, with a plate voltage of 450, I had it set for 42 mA, I bumped it up to 53 mA.

It actually sounds worse than it did yesterday.

I went through and re-flowed some components, I still have bad distortion.

Any ideas?

[sluckey]

It actually sounds worse than it did yesterday.

I went through and re-flowed some components, I still have bad distortion.

Any ideas?

Yes. Roll back to March 6. No Trem-O-Nator for you!   

Seriously, put it back like it was. Still have bad distortion?

[purpletele]

It actually sounds worse than it did yesterday.

I went through and re-flowed some components, I still have bad distortion.

Any ideas?

Yes. Roll back to March 6. No Trem-O-Nator for you!   

Funny guy!!  It is kind of funny though, I was excited and the trem works so nice.

Seriously, put it back like it was. Still have bad distortion?

I had figured that might be the next step.  If I still have bad distortion then I'll start getting bummed, this amp was really nice at one point. 

I think I'll crank up the Dual 50 and Jam for a while.  My Theater project got shut down today so it feels like 2007 with a twist!
 

[sluckey]

I think it will be good to get back to a baseline condition and evaluate the distortion issue. The mod is simple and easy enough to reinstall later. We need to know if the mod actually caused the distortion for you, or if it is truly just collateral damage and if rollback will cure the distortion. Rolling back should not be too difficult. Don't bugger up the trem o nator parts.

Don't forget to use your 250K int pot. And put that 47K resistor back if it's not worn out.   

[purpletele]

I think it will be good to get back to a baseline condition and evaluate the distortion issue. The mod is simple and easy enough to reinstall later. We need to know if the mod actually caused the distortion for you, or if it is truly just collateral damage and if rollback will cure the distortion. Rolling back should not be too difficult. Don't bugger up the trem o nator parts.

Don't forget to use your 250K int pot. And put that 47K resistor back if it's not worn out.   

3/4 the done, thanks for the 250K Pot reminder, I'll finish up with that everything tonight, and re-check in the morning.

I was so excited I bought a case of the Vactrol LED's!  I thought it would be a slam dunk of swirl. 

I bought enough parts to upgrade my Princeton and two Deluxe's so I should be covered.

[shooter]

it feels like 2007 with a twist

I was thinking more 1984, with twisted sisters singing do-wap 

[sluckey]

I was so excited I bought a case of the Vactrol LED's!  I thought it would be a slam dunk of swirl.

I'm optimistic that you will still get to use them.

[purpletele]

The retro Mod work went well.  I took my time and tried to be very accurate.  The results did not turn out very well.

I have very bad distortion and I cannot get the tremolo to work.  I replaced the footswitch jack back to the RCA, replaced all of the original components including the 250 kL Pot. 

I went from having mild distortion to significant distortion.

So it is apparent that there is something I did to cause the original mild distortion, and I think I compounded it.

I'm having a Soup Sandwich for lunch.

I'll take a fresh voltage reading in a few after I take a break.

Update

I made a mess, some of my voltages are wonky, I have a place to start looking.  I spent some time cleaning up the B+ Resistor Connections, the 1K Resistor connection was suspect.

Note: I picked up the turret connections at the dual .1 caps that were previously separated with the mod.

[tubenit]

I'm following this with great interest. I am not sure what schematic you are working off of?  In it's current state as of reading this post, can you share a schematic of exactly what you have now?

Is it closer to the Hoffman schematic that Sluckey drew up OR   closer to Sluckey's Tweed Deluxe but with tremolo added?

IF you found wonky voltages, that's certainly a good starting place to trouble shoot.

With respect, Tubenit

[tubenit]

Is the green column your current exact voltages?   IF so, the LTPI V5-6 plate voltage looks way off. 

Something has got to be amiss there? You might want to recheck that plate voltage on V5-6 and on V5-7 &  V5-8 cathode?  I am wondering if there is a bad connection on the pin or on the board that goes to pins V5-7 & V5-8? I'm wondering if a bad connection there is not drawing down the voltage on the plate properly?

With respect, Tubenit

[purpletele]

Is the green column your current exact voltages?   IF so, the LTPI V5-6 plate voltage looks way off. 

Something has got to be amiss there? You might want to recheck that plate voltage on V5-6 and on V5-7 &  V5-8 cathode?  I am wondering if there is a bad connection on the pin or on the board that goes to pins V5-7 & V5-8? I'm wondering if a bad connection there is not drawing down the voltage on the plate properly?

With respect, Tubenit

Jeff,

Thanks for the interest. 

The current status and trouble shooting theory is to pull the Trem-O-Nator Mod and replace the original circuit.  This was done to prove that I have a collateral damage distortion issue from the TON mode.

I am using the original Hoffman AB763 Schematic.

After I installed the Trem-o-Nator Mod I ended up with a mild distortion on the lower register.

It was agreed that I should replace the circuit to original as stated.  I took my time and tried to be very accurate, but I fouled something up.

Currently, the amp is up and running.

The Green voltages are from last evening and I haven't done anything yet.
V5-6 and V5-7 and V5-8 are definitely wonky.  It is confusing to see those voltages on V-5 way off, I hadn't molested anything on V-5, but I am never surprised of the results that I can produce.

It is certainly a humbling experience.  I am going to gear up and spend some time going over V-5 for starters.

I had changed the B+ 3Watt resistors twice and that move made me suspect the Power resistors. 

Mode Voltages
A = 437 V
B = 436 V
C = 431 V
D = 418 V

Note, the amp was preforming very well and sounded fantastic before I hacked it up.

Thanks,  BV

[sluckey]

Looks like the wiring to V5 socket is really messed up. Rewire IAW the layout.

I'd really like to see a bigger hi-rez pic that clearly shows V5 socket, the board, and all wires between the socket and board.

[tubenit]

I'd really like to see a bigger hi-rez pic that clearly shows V5 socket, the board, and all wires between the socket and board.

+1

[purpletele]

Looks like the wiring to V5 socket is really messed up. Rewire IAW the layout.

I'd really like to see a bigger hi-rez pic that clearly shows V5 socket, the board, and all wires between the socket and board.

OK

See below. 

V-5 is the third photo, the last is V4

[purpletele]

Two more of the V4, V5 section

[shooter]

If I'm reading your Vchart correctly it appears your bias is twice what it was, not sure if that matters, but maybe tweak it back to the "good times" 

[purpletele]

If I'm reading your Vchart correctly it appears your bias is twice what it was, not sure if that matters, but maybe tweak it back to the "good times" 

The good times are gone apparently.  Turning the bias down created more distortion, cranking it up was better but I was about 100 mV. 

After I took the photos I thought I spotted a couple of tube socket connections that didn't look great so I cleaned them up, but it didn't change the voltage readings or performance.

I have multiple passes through my wiring at V-5 and V-4 and I'm not finding any incorrect wiring so far. 

Dinkyguitar should review this thread before he starts a JCM 800 on a PCB,  my board is getting beat up now and I am concerned that I may have had a cold joint that caused the distortion and I have compounded it.

[shooter]

guessing 6L6?  50mV seems good, 100mV might not be

since the trem is "gone", steal the tube and swap it in the PI slot.

[purpletele]

guessing 6L6?  50mV seems good, 100mV might not be

I have JJ 6L6 GC.  I had a Plate V of 450 and I had the bias set at 53

since the trem is "gone", steal the tube and swap it in the PI slot. That was a great idea!!  No change

[shooter]

No change

ah, newbie, there is a change, it ain't the tube, check! 
you also wiggled all the pins good, so if by "no change", then we can make a small assumption (knowing the risks:)
the socket n wiring are maybe ok IF your voltages stayed the same.

what happens to the low plate voltage when you have the PA tubes out?

[sluckey]

AB763 wants a 12AT7 for the PI. If you gotta steal a tube then steal the reverb driver, which should also be a 12AT7.

And change the V5 wiring to agree with Hoffman's layout!

[purpletele]

No change

ah, newbie, there is a change, it ain't the tube, check! 
you also wiggled all the pins good, so if by "no change", then we can make a small assumption (knowing the risks:)
the socket n wiring are maybe ok IF your voltages stayed the same.

what happens to the low plate voltage when you have the PA tubes out?

With V1 thru V5 out I get 435 V

[purpletele]

AB763 wants a 12AT7 for the PI. If you gotta steal a tube then steal the reverb driver, which should also be a 12AT7.

I used a fresh 12AT7

And change the V5 wiring to agree with Hoffman's layout! I'm not seeing it,  I have V5-6 and V5-1 tied to the .1 Caps in the PI
V5-2 goes to the 1m resistor.
V5-3 and V5-8 are tied together and connected to the 470 ohm resistor
V5-7 is tied to the small cap and 1m resistor.

I highlighted and traced it again a few times, I'm just not seeing an error at V5 wiring.

What looked incorrect to you?

[sluckey]

Sorry. Disregard. My eyes must be blurry.

Now measure resistance from pin 7 to chassis. Also measure resistance across the small cap (C23) that is connected to pin 7. What have you?

[purpletele]

Sorry. Disregard. My eyes must be blurry.

Now measure resistance from pin 7 to chassis. Open Load

Also measure resistance across the small cap (C23) that is connected to pin 7. What have you?  Open Load

[sluckey]

Getting close! Both of those readings should be approx. 1MΩ. Check R44.

[purpletele]

Getting close! Both of those readings should be approx. 1MΩ. Check R44.

I am getting 1 meg while in circuit

[sluckey]

Check R42.

[purpletele]

Check R42.

21.8 K

[sluckey]

Recheck the resistance across the small cap (C23)

[purpletele]

Recheck the resistance across the small cap (C23)

Open Load

[sluckey]

You do realize that the 1M ans 22K resistors are directly across that small cap? But yet the 1M is OK and the 22K is OK. Resolder all four of those turret lugs and recheck the resistance across the small cap.

BTW, I can stay online with you for another 45 minutes if you want to stay online and solve this mystery.

[purpletele]

You do realize that the 1M ans 22K resistors are directly across that small cap? But yet the 1M is OK and the 22K is OK. Resolder all four of those turret lugs and recheck the resistance across the small cap.

BTW, I can stay online with you for another 45 minutes if you want to stay online and solve this mystery.

I'll take the slot of time, thank you.  I took the readings without power.  I'll float those turrets.  I don't understand how I would show resistance in that cap?

[sluckey]

Please tell me you did not remove the cap to check resistance across it!

[purpletele]

Please tell me you did not remove the cap to check resistance across it!
No I did not pull the cap, I floated the turrets and got a reading of 1 meg from pin 7 to chassis and 1 meg across the cap.  I'm putting the tubes back in to see where I'm at voltage wise.  Pretty incredible CSI work

[sluckey]

That should fix the wonky voltages. Hopefully it will fix the distortion too. Still got 20 minutes. I'll be right here.

[sluckey]

Signing off. I'll tune in tomorrow. Hope you have some good news.

[purpletele]

Signing off. I'll tune in tomorrow. Hope you have some good news.

Great news!  Distortion seems to be gone, I cranked it and it seems solid.  The trem doesn't work, but I can see how destructive it can be to randomly refloat things. 

The plate voltage is 436 and I set the bias at 48 mV.  The voltages for V5 are back to normal.  I posted the voltages for V-5

If we can conclude that the Trem-O-Nator was not causing the distortion, then I will take a break and then re-install the TON tomorrow after I file for Unemployment.

Steve, Jeff, Shooter, et al..thank you taking the time to guide me again.  It's beer time

[sluckey]

Great news!  Distortion seems to be gone, I cranked it and it seems solid.  The trem doesn't work, but I can see how destructive it can be to randomly refloat things. 

If we can conclude that the Trem-O-Nator was not causing the distortion, then I will take a break and then re-install the TON tomorrow after I file for Unemployment.

That is good news. Play the amp for a while to be sure you know how it sounds and be sure the distortion is gone. I never thought the TON mod caused the distortion. Always thought it was something unrelated that happened while you were doing the mod. That's called collateral damage.

Once you are happy with the amp again you can proceed with the TON mod. Hopefully it will go as expected this time. You can probably do it blindfolded by now! 

BTW, see the attached pic for the most logical reason that your trem is not working right now. It's not necessary to fix this unless you just want to be sure it works and get a fresh idea of how it sounds before proceeding with the TON mod.

FYI, that last pic you posted was the sharpest pic yet. Made troubleshooting much easier. I'll stay tuned...

[tubenit]

Hooray success!!!!   

Man, you stuck with it and your tenacity and persistence prevailed!!

I think the TON mod will work flawlessly for you and not cause any unwanted distortion.

Continuing to follow this with interest!   Jeff

[shooter]

It's beer time

that's why I quit talking last night! my "beer" is pretty stout 

way to hang in there on a problem, you're gonna be a rarity, you can play both in and out of an amp with confidence 

[purpletele]

Thanks again guys.  The amp plays very well, so I think it has a clean bill of health to try and withstand another Mod.

Just got in from a deserted jobsite, weird feeling about that.  I'll play it for a while and possibly start the ReMod this afternoon.

BTW, good eyes on the 4.7 K resistor Steve! 

[purpletele]

I played the amp for about an hour and it seems fine.  I will need to address a little overpowering Reverb or maybe the linear pot in the future.  I can only set it on 2 before it gets really caverness.

I have an updated voltage chart for reference.

Steve, I have a question on the TON Hoffman layout.  Should the .01 cap that is in series with the .022 be changed to a .022 per the Bandmaster schematic?  I have attached the schematic behind the AB763 Layout.

I had used a .022 in lieu of the .01 in my previous TON mod.

Thanks

[sluckey]

Ain't no big deal. Either cap is fine. The .022 will give a slower speed (swamp), .01 will give a faster speed (Fender norm). If you want to get fancy then put a .01 on the board and use a switch to put another .01 in parallel to the onboard cap. I've done this on several amps. I didn't do it on the Bandmaster because I didn't want to drill any holes.

[purpletele]

The Trem-o-Nator Remod went swell!

No issues of distortion after a couple playing sessions.

The reverb has always been super sensitive where I can barley get to 2 before it goes into some deep caverns.  I am using a 100K linear taper pot as designed.   My 2nd Deluxe is like that as well.

Any advice on the Reverb would be splendid.

Thanks

BV