Could someone glance over/proof my mods layout plan? BFPR new build...

[PeaveyBandit]

Does anyone have a spare moment to look over my AA1164 Princeton Reverb Mod layout? I'm building this from parts and just about to start loading up the circuit board as soon as some final parts arrive next week. It's coming together nicely.

Mods are highlighted in color on the layout but let me list them anyway. I got most of these ideas from here but I've also been researching and trying to do my homework to better understand what these mods do.

1. Stokes mod moving to other power supply node
2. Paul C, converting bias on PI
3. Rick E mod changing resistor on power supply to 4.7K to change voltage
4. Added grid resistors to 6V6's
5. Using GZ34 rectifier
6. Upping NFB resistor to 5K
7. Lowering reverb resistor from 3.3mb to 2.2mb
8. 100 resistors on filament and remove green-yellow centertap from ground
9. Copied from Hoffman Amps site the 10KL pot/resistor/cap change for adjustable bias control.
10. 12" speaker
11. Deluxe Reverb OT


See Layout attached. I'm a little concerned about the adjustable bias mod and the values that change on the capacitor up to 47uf and also the 10KL pot and 27k resistor make it hard for me to understand how that can cover the range of the stock 22k resistor only and what I can adjust that to before power up. I'm even thinking about firing the amp up without that mod, measuring the voltage and somehow working from there before I install the adj bias mod.

STANDBY SWITCH MOD? - I'm also real curious how I might safely add a standby switch in place of the ground polarity switch. Not in general terms but exactly which points to cut and any components I might need to add. For example would it need a choke then?


Reference previous forum topic thread I started on this topic

[Bruce / Mission Amps]

What power transformer are you planning on using?
Remember the stock PT was a weanie at around 70-90ma max.
Most reissue PTs are based on the silver face years... with a GZ34/5AR4, your B+ might be really higher then you want with this amp.

With a quick look over, I didn't see anything wrong with what you drew out for the mods.

I'm not so sure about lowering reverb mixing resistor from 3.3mb to 2.2m.
I've found in the past that the stock RC combinations to be pretty good and allows the amp to be very versatile with respect to clean and driven wicked. Just experiment with those values.

The modded bias supply is based on using a generic, slotted wiper shaft, full size bias pot and those are only 10Kb.
This is all variable and depends on what power tubes, PT and rectifier combo you use....
With the 10Kb pot set to min resistance, I would think it is possible that the 27K resistor will have the bias "set" voltage slightly deep and your power tubes might be running a little cold.
With higher B+ voltages found in vintage amps running at new mains line voltages of anywhere from 120v to 126v, ... I use a 22K-25K trim pot in series with a grounded 6k8 to 10K resistor on my modded PR amps.
That seems to give me enough range to get the power tubes idling at 7 watts to +10 watts easily.

Always set your bias voltage for the max negative voltage on the power tube grids before applying B+ to the tubes on a fresh build.

Your Deluxe OT can handle the tubes idling at the higher ranges but I'd be careful with the stock power transformer specs.

Standby, just cut the lead from the rectifier (lug 8) to the first filter cap and insert your standby switch there....

Also, POWER tube sockets:
Pull the grid leads off lugs 5 and insert a 1k5 1/2 watt resistor on lugs 5 to lugs 1 of the power tube sockets. Reconnect the grid lead wires to the lug 1 side of the 1k5 resistor.

[PeaveyBandit]

Bruce thank you!!!

Yes it's a new Heyboer PT from AllenAmps and beefed up. Same source for the deluxe OT.

I'll add the 1500 resistors too. I wondered about those.

I'll have to take your advice on the bias and start cold and find the right values that make the tubes run right. No problem, I'll just have to experiment to get that right I guess, to find the right sweep and range. I've been reading more about it and making more sense now.

Thanks again!! Priceless!

PB


POSTED EDITED NEW VERSION OF LAYOUT