Need Help in Tweaking my Peavey Pacer/AB763 Deluxe Reverb Conversion

[Platefire]

Regarding locking pots, no this is not a locking pot but one thing I do sometimes when I don't want a pot to float out of adjustment is put on a type knob with a tension set screw and allow  the bottom of the knob to drag against the surface(pickguard or chassis). It will still turn but the drag keeps it from drifting. That's what I had in mind on this or you can just leave the knob off and that will usually allow the setting  to stay in place. That setting would be something I would check every time I use it on start up. Anyway this NFB setup would allow me to get three different things (1) fully disconnected NFB (2) adjustable NfB up to 50K (3) Stock DR setting(fully clockwise)

On the speaker, since I've tweaked the amp with lower D rail voltages, installed the 47 NFB resistor to ground, rewired the mid/raw pot, it's been sounding great to me with the existing 25 watt Weber. This Weber was a special design by Gerald W for users of the Silvertone 1482 for folks on the now defunked Vintage Silvertone Forum. I ended up putting a Emi Cannabis Rex in the 1482 and put the Weber in my DIY DR. I haven't dropped the new speaker Idea, but with the amp sounding better, it's less of a priority. The Wizard and the 12C/S are good prospects to try. I've been jamming on it everyday and what a pleasure! Pure Fender tone at its best. Platefire

[Ed_Chambley]

Well it is great to hear you you have it tweaked.  It is really a great all around amp.  I guess when it began to loosen up some.  I mean you play 5E3 and such which are greasy feeling and even the JTM45 feels a little like that as well.  But modding a blackface where you can get that gritty sound and easily return to a Blackface Fender is what I have always preferred in a club type amp.

I like Weber Speakers and have a lot of them. 10A125 (20watt) and 10F125 (30 watt), 2 twenty watters on top and ceramics on the bottom in s super reverb is the best speaker setup I have every heard.

Thing is I think you are saying the amp is feeling familiar and you are beginning to grow an attachment to it.

KEWL BEANS BOB!

[Platefire]

When I built this amp in 2008 it was such a long drawn out affair planning and making everything fit in that Peavey Pacer Chassis/Cab that I apparently didn't have any tweak left in me when it was finally done. So I eventually begin to realize it wasn't quiet right. I played a Silverface DR in the 70s that sounded great, so I knew it was suppose to be good, even though I never played the Blackface circuit. So here 7 years latter I'm finally getting around to the tweaking  and it's now sounding like the DR I remember. 

This amp is kind of special though, because it is the last remaining piece of equipment from the old days. The old SS circuit use to rock pretty hard with the OD control activated by a foot switch(like another channel). It was a loud 45 watts. So the new plan was to retain the old Peavey Pacer look but being incognito for a DR lurking underneath. A casual observer would never know. The letters/symbols on the front face of each original  control knobs tells what the true function of the pots are in opposition to what the old original face plate indicates. I actually have a legend(see pix) on the back of the chassis that spells out the operation of each knob for who ever ends up with this amp after me. So this amp is so personalized that anybody else would have to study it and figure it out before they could properly operate it. This has to be one of the weirder conversions in guitar amp history ---regarding hidden cosmetic identity not the circuit. 

I got the the parts in from Doug today to try a 100KA pot for the reverb and try my switchable pot idea for a NFB control. If those tweaks work out like I hope, that should be it for the circuit. I'm trying to be patient, take my time and do it right this time. Platefire

BTW-I've already got my line worked out what I will say when someone says "That's a fine sounding Peavey" I'll say "yelp, it sure is".

[Platefire]

I've got the amp all put back together. Satisfied that everything is good. I did try the 100KA pot on the reverb and it did give me more travel adjustment but I liked the sound of the 100KL better so I ended up putting it back in. Putting the 22/50 cap on the tremolo cathode livened the intensity up where I am real happy with that. Last but not least, the NFB switchable pot works really well. I took some pixs that is attached. It's a shame I have waited this long(since 2008) to make these changes but as they say "it's now or never". Got one sweet DR now. Thanks for your help! Platefire

[sluckey]

I did try the 100KA pot on the reverb and it did give me more travel adjustment but I liked the sound of the 100KL better so I ended up putting it back in.

Can you describe the difference in sound between the 100KA and the 100KL pots?

[smackoj]

Pfire; would you be up to making the changes on your schemo and posting it? would be nice to see the 'finished' project with your tone tweaks included.

gracias   

[Platefire]

On the 100K A and L pots. To me the "A" sounded brighter and some of the previously earned warmth seemed to be missing. Also the reverb sound changed in a way I'm not sure how to describe but was less favorable as I remembered the L pot. I reasoned with myself, this can't be! Just the difference between Liner and Audio taper couldn't do this? After playing on it several times between breaks and coming to the same conclusion every time, I finally decided I may as well change it back or I wouldn't be satisfied. So that's what I did and was happy with the sound when I changed it back. I have no logical explanation why or how it could be that much difference in the pots? Bottom line is you have to follow your own ear and instincts on something like that, even when it don't make sense.

Attached is the revised schematic. De Nada, Platefire

[SILVERGUN]

Bottom line is you have to follow your own ear and instincts on something like that, even when it don't make sense.

Just the fact that your ear can tell a difference is a good sign at any age, and just because it doesn't make sense doesn't mean it ain't better.
 
Since your an obvious connoisseur of the finer nuances of reverb, I've got a couple tweak ideas that have not been mentioned yet in this thread.
 
- Change the 500p cap that feeds the input of the reverb driver to .001 to allow a little more mid body into the mix, and maybe sound warmer to your obviously seasoned ears (got that one from tubenit)
 
- Try removing the bypass cap on the reverb driver 12AT7 to calm down the wetness of the reverb. (from PRR)
If you could hear the difference between an A pot and an L pot, you'll definitely hear these differences.
This mod will give you a wider useable range on your reverb pot, and dampen the overall wetness of the reverb.
Both tweaks together made their way into my last build.
 
Either way, I've enjoyed hearing the results of your tweakin'

[Willabe]

Just the difference between Liner and Audio taper couldn't do this?

I'd measure both those pots for resistance. Maybe their way off from 100K?

It might be harder to dial in the verb with A taper but brightness/warmth difference seems odd.

[Platefire]

Thanks for the tips on the Reverb but truly I'm really happy with the reverb sound. The only thing that was bothering me  is that I was getting my reverb sound at 1.5 where normally I have to turn up to about 3 or more. So no problem with the reverb sound. The short amount of travel conflicted with my previous fender type reverb settings experience. That's what sluckey was trying to help me by suggesting using the A pot---more travel to get the same thing but the problem is it didn't sound the same to me and I kept missing my previous sound. So I had to go back and get it! So I'm totally happy with my reverb sound, so no need for tweaking any further. I can re-calibrate my fender reverb experience for shorter travel tweak on this amp.

The truth is I'm loving the sound and feel of this amp now so much that I don't want to do anything to interfere, disturb or change it---if you know what I mean! I've got the amp buttoned up and can't see no reason at this point to tear it down and resume tweaking. I've noticed it's even quieter regarding operation noise also and I love a quiet amp. So I ask for help on tweaking this amp and all of you came through and pointed me in the right direction. You know previously I wouldn't even play this amp because I just wasn't happy with it and avoided it. So now I'm very pleased with it and certainly won't be avoiding it anymore. I thank you ALL very much for helping me get there!! Platefire 

[SILVERGUN]

The truth is I'm loving the sound and feel of this amp now so much that I don't want to do anything to interfere, disturb or change it---if you know what I mean!

Oh, I know what you mean....I felt the same way after I built a cathode biased version of sluckey's TDR and tweaked it to perfection....

Only problem was, I built it for someone else and hated to give it up. There really is something to that circuit.
 

[Platefire]

Well!!! It's time to make a TDR for yourself---and if someone buys that, then another one

[Platefire]

I made a removable panel to make it a closed back cab. The two top keepers rotate to hold the top in place securely.
I'm just wondering if the opening on the top back plate panel at chassis is enough to let the tubes breath sufficiently? Just finished it, so I will jam a little to see what it sounds like. I might aught to get my infra-red thermometer out and watch the temperature on the tubes. Platefire

[Platefire]

I'm really liking the sound of the amp with the added back panel on. Best I can tell added a measure of bass, little louder and little more responsive is the effect I'm getting---for bedroom jamming adds up to additional layer of sweetness--and that is good. Not sure how that would pan out in live band situation? The rectifier and 6V6S's are running around 190F in the hottest spot---that's not bad is it? The added back panel is not air tight--has openings for power cord, trem/reverb cord plus a small 1/16 crack at top where it joins the bottom of the top back plate.
   If this added panel works out, I'm thinking of added one to my Allen Accomplice. Platefire

[Platefire]

I picked up a small 4" fan at Wally World today that is 120VAC with a regular power cord. I thought by just looking at the swivel stand in the store that It should be able to hang on the upper back panel. When I got it home and tried it, sure enough it hangs fine.  So at the least it's a good temporary solution to restricted tube ventilation when the closed back panel is installed.


EDIT: haft to say I've been trying the amp with the closed back panel on and off. With the strat I'm using sounds much better with it on. The response/touch feel/sustain is much improved at the same volume/tone settings with it on and just a little warmer tone. The fan is doing an OK job of keeping the power tubes and rectifier cool. I was a little concerned the fan would effect the speaker with a fluttery sound but best I can tell it's not. I'm thinking that the close back panel is a + for the DR sound. 

[Platefire]

I know it's time for this thread to go away but----took the amp to the Church, set it up to play with the Praise Band and used it this weekend. I wasn't disappointed. I used my tele, the brightest worst case scenario for brightness and ice picks. I was able to set the amp to mellow it down to where it was a sweet tele. If this amp can smooth out a tele all my other guitars will be a cakewalk. I never trust my own bedroom amp assessments much until I put it through a live band playing situation that to me is where the rubber meets the road. Passed with flying colors! I'm a happy camper---Thanks, Platefire   

[sluckey]

Another happy ending.   

[Platefire]

Sorry! Had to add one last finishing touch to this documentation. I just labeled my NFB control and added the pixs of it in it's normal AB763 Blackface position and NFB off position. Everybody can go back to sleep now

[ac427v]

Inspirational!
How did you do the lettering? I need to do some back panel lettering on my next amp. I've done dry transfer letters, one at a time. I was not been happy with my spacing. Yours looks so professional!
Craig

[sluckey]

You can get sheets of dry transfers that have common audio and electronics words on them. Much easier than individual alpha/numeric sheets. Platefire used a label printer with black text on clear tape.  Dymo and P-Touch are two brands I've used.

[Ed_Chambley]

I use a Brother P-Touch with clear tape.  Looks like this.