New build....HRD to AB763 using existing transformers

[Shack]

I know that it would have a bridge rectifier instead of the original power supply, but I think I can build a convincing blackface style amp in there , I would like to use a turret board that uses the classic Fender layout, just not sure yet if there is room for a doghouse or extra tube for reverb. I dont need tremolo, so it would use 4 preamp tubes, and 2 power tubes.One channel.

Any helpful input before I gut the amp?

[tubeswell]

Any helpful input before I gut the amp?

Gutting this type of amp to make an AB763 would be a good idea

[jordan86]

I've not done it, but my buddy just gutted an old PCB Deluxe Reverb and replaced it with a hardwired board. Sounds GREAT.

Downloaded some pics online. Looks like you got ample real estate on that chassis. I think the you have a perfect little spot for a 4th preamp tube between the 2 and 3rd tubes. Plenty of room for a doghouse on top of the chassis as well. Looks like you could go tube rectifier possibly. There's room on the opposite side of the power tubes for a rectifier tube socket it looks like. But I am guessing the PT doesn't have a tap for it.

The AB763 Bandmaster is solid state rectified so that would be a good schem/layout to cross-reference (copy). As far as single channel goes, RobRobinette has a 6L6 Blackvibe but it is tube rectified. That's prob the closest schematic/layout for what you want. https://robrobinette.com/RR763_BLACKVIBE.htm#Blackvibe_Reverb

Hoffman and Sluckey both have single channel ab763 options, but I think they either have 5 preamp tubes (+Vibrato) or are stripped down without Reverb.  Some of the more experienced guys here would know.

I'd say its definitely possible. Could grab a small parts kit from either Hoffman or Mojotone to make it easier.

[Shack]

I figured because I have a tank and reverb tranny from a previous build, that adding a 4th tube would be cool, and the HRD has a huge chassis, so if planned right, it would be way worth the project.

If Sluckey remembers me, the amp I built like 4 yrs ago was from a gutted 70s Peavey vintage, using the trannys available. It has been my main amp for that time and the HRD has sat unused. I built a plexi/bassman 100 watt amp out of it, and it is awesome.He helped me iron out any issues I had, and was very helpful.

I need to find the turret board with a classic fender layout, a bias board, and a power supply board to use, and a way to mount the tubes without a PCB .....a faceplate would help too, just not sure how to do all of this and im not familiar with diylc yet

[jordan86]

For further reading on “how to” there are at least five other threads in here discussing the exact same thing. Check those out. Hoffman should have all the parts you need, including tube sockets. If not, a Mojotone small parts kit for a twin reverb or super reverb would have the parts (minus the custom turret board).

[Shack]

It appears to me that the board for Robs Blackvibe is close to Fender layout, I would like to order the bias and filter board from the same layout but the diylc anylizer wont seem to let me... and I dont know alot about the program

[sluckey]

Any helpful input before I gut the amp?

Measure and record voltage for every filter cap, including bias cap. Measure and record voltages for pins 3, 4, 5 for both 6L6s.

DON'T LOSE THIS INFO!

If you use a Hoffman AB763 board you won't need a doghouse. Just install the filter caps between the board and the pots. You would want his type 2 bias board with a slight wiring mod to accomodate the FWB rectifier diodes.

[Shack]

will do thanx.....and btw.....im watching Dougs you tube videos, what a cool program 

[Shack]

so I got the voltages all wrote down, and started gutting.......my old amp tech replaced the output tranny and this replacement has alot of secondary wires ....

primary wires are ovbiously red, brown and blue

secondary wires are ....green, green/yellow, yellow, black and black/yellow, with a couple other wires taped off under the transformer,lol.
they all go to the ext jack along with feedback wire, and a green jumper to the main output jack.

I would imagine that I would just use the green and black for a single 8 ohm speaker jack.

The isnt a single number on this transformer for me to look it up and I cant find the old manual with the repair invoice in it.

Can anyone shed some light on it for me?

In the meantime , ill get ready to order my turret boards.

[sluckey]

Ask your old amp tech.

[Shack]

That was a great idea.....its an older hammond interleaved transformer...he told me how to wire it

[sluckey]

May be similar to this OT. Look on page 8...

     http://sluckeyamps.com/VAC15/Vox_AC15.pdf

You can find this same info on the Hammond website.

[Shack]

exactly the same wiring scheme....

[Shack]

Whats the best way to add tube sockets to the existing holes? they are 1 inch in diameter for preamp tubes.... not sure about power tubes yet

[sluckey]

Maybe this will give you some ideas...

     https://el34world.com/Hoffman/Pro_Junior_Build.htm

[Shack]

I have Belton sockets on the way......I prefer those anyhow. hopefully they can be used in those holes, and I will make a 4th hole as well . Seems, I already had a Hoffman eyelet board for an AB 763 with normal channel removed, so now I will decide between that board and the RR 763R turret board and have a spare for another build. Can I bolt the FWB rectifier to the chassis or should I mount it on a board? In my other amp I bent the leads and mounted it to terminal strips.

[sluckey]

Can I bolt the FWB rectifier to the chassis or should I mount it on a board? In my other amp I bent the leads and mounted it to terminal strips.

Your choice.

[Shack]

I decided that the pro jr way of doing sockets is the best way to go

[Shack]

So im nearing the finish line.....I went with the socket mounting similar to Dougs Pro juniors....I might want to use 1/2 inch number 4 bolts rather than the 1/4 inch ones, so I can use a lock washer on there to prevent vibrations from loosening the nuts off....the 1/4 doesnt give much meat for the nut to grab.

I also installed a type-4 master on it, only to realize that using Ken Fischers instructions is intended for a Marshall type preamp, rather than a Fenders...so I need to figure out whether to lose it or move it.

Is there a more modern way to post pics, other than loading to PC and resizing?

I really hope this sounds like a BF Fender....cause it will be cool....and im not worried about the SS rectifier, I seem to prefer those for the tones I chase.

[Shack]

Well, I finished her today, was proud of myself foe working out the initial bugs without pestering Sluckey..( grounded the 3.3M reverb resistor, oscillation between the volume pot and grid, etc.)

The only issue I have now is notes seeming to distort as they trail off, and its worse the louder I turn it up. My 2 input jackset didnt seem to work either, will have to double check the wiring.

I am using a different speaker and a set of older tubes, which I will replace to see if the distortion goes away, but was wondering if anyone has any ideas of another cause to investigate?

Thanks

[Shack]

Any helpful input before I gut the amp?

Measure and record voltage for every filter cap, including bias cap. Measure and record voltages for pins 3, 4, 5 for both 6L6s.

DON'T LOSE THIS INFO!

If you use a Hoffman AB763 board you won't need a doghouse. Just install the filter caps between the board and the pots. You would want his type 2 bias board with a slight wiring mod to accomodate the FWB rectifier diodes.

filter cap      1         2        3        4

hrd           421     419     410     362

now          422     422     413     389


                            pin      5        4        3                       5        4        3


inside  6L6                   -42       419     419       was       -46     444    446

outside6L6                   -42       419      419                  -46     445    447



                           pin      1           3              6            8

v1                                364        1.8            273        1.6

v2                                413        8.4            413        8.4........reverb driver

v3                                248        2.1            271        2.1

v4                                230        96             217         96........PI


These are my voltage readings , does everything look ok?

[Shack]

https://prntscr.com/10ykh0c

[Shack]

One last thing.....this amp sounds real good, real Fendery, but....

It doesnt take well to OD pedals in front like I would think it would...they sound a bit fizzy, and I dont turn the gain up on my pedals that high.

Possible reasons

1. 1k feedback resistor instead of 820 ohm
2. lead dress issue
3. preamp tube
4. maybe biased too hot....I have it at around 40 ma

Is there anything else I could look into?