BFPR Clone "just fishing"

[frankeg]

Since re-capping my friends Princeton -67 stock except with 12" Celestion V30 mod, I haven't been able to get that sound out of my head so I've decided to build one. I've built kits before so I'd rather do this from scratch with top shelf parts. I'm fishing here for thoughts/ideas to make this project really special. I know there are a lot of builders here who know the PR very well so please chime in... I'm thinking I'll upgrade the PT but not too sure if i want to change the OT. Any thoughts on cap can recommendations, coupling caps (orange or mallory) and quality pots would be appreciated. Thanks in advance...frankeg

[tubeswell]

I did mine with an IRF820 source follower after the LFO triode (using the same circuit values as the cathode follower stage in the 5G9 trem circuit). Trem sounds really smooth that way, and the extra parts didn't take up much space. I posted the schematic somewhere.

[MWJB]

Princeton OT's are a weak point, I'd build it using BF Deluxe spec trannies (PT will need a bigger cut out) this will also allow a switch to 6L6s if so desired. Don't use a cap can, use discrete filter caps, ground main & screen caps to a PT bolt, ground the others to the input jack (each cap gets it's own wire), use 500v rated caps min - if building from scratch I'd even wire the main caps as a totem pole, series arrangement (see AB763 super Reverb). Use a 100v rated bias electrolytic.

The amp will work fine with either Mallory's or orange drops...that's entirely up to you.

[frankeg]

I followed your build thread and gleamed so good info. Thanks tuneswell

[frankeg]

I've heard good things about the OT upgrade and am leaning that way but I don't want to alter that PR mojo too much. I also like the idea of discrete caps - I trust them more. Thanks MWJB... I've followed peaveybandits build as well and will go with higher voltage to the PI but not sure if I want to mess with the PI bias mod - is any PI truly balanced? any thoughts there?

[MWJB]

"is any PI truly balanced? any thoughts there?" Yes, cathodyne PI like in the PR is balanced (match the 56K resistors at plate & from cathode to ground), as is a proven LTPI, as is a self split (SIPP) output. There is a lot of hogwash written about how guitar amp PI's aren't really balanced, most are balanced perfectly well, so much so that an imbalance in power tube plate current is easier to detect. You normally have to start changing component values from stock, to achieve an audible imbalance. Cathodyne PIs, LTPI & even paraphase PI's are seen in hifi amps.

[frankeg]

(match the 56K resistors at plate & cathode to ground) That makes sense to me. So you wouldn't do the fixed bias mod on the PI just go with matched components? I read an article in Tone Report where the author recommended matching the power section but he wasn't specific on any components...

[MWJB]

"....just go with matched components?" Yes.

[Casey4s]

I built a BFPR (Variation) a few years ago. I like big transformers for a given application so I used a Deluxe Reverb OT on my PR build. I used a Hammond 272FX for the PT.

Best of luck with your build. Good planning is a great way to start.

Link to my BFPR build pics. (don't look for a "clone")

DIY BF Princeton Reverb Variation Walnut pictures by Casey4s - Photobucket

[frankeg]

Thanks MWJB. As aways I appreciate your help....

[frankeg]

Hi Casey, Nice job! Do you like your sound? I've used mallory coupling caps for my other builds but am pondering the orange drops like you have. I am also going for the upgraded transformers. I will probably go with the Allen trannys since they will fit the chassis with minimum change. Thanks...

[Casey4s]

Hi Casey, Nice job! Do you like your sound? I've used mallory coupling caps for my other builds but am pondering the orange drops like you have. I am also going for the upgraded transformers. I will probably go with the Allen trannys since they will fit the chassis with minimum change. Thanks...

I have always used mostly orange drops in my amps and I like working with them and have never been disappointed. I am going to use a mixture of ODs and 150s in the tone stack of my next build just to make a few changes.

[frankeg]

I've decided to do an eyelet board using G-10 Linen not fiber and I'm going to size it 3-4" longer depending on how it fits, to have room for my PS caps. I bought most of the components through Doug Hoffman and am using 1% mf resistors. I have a mix of caps. Electrolytics are all Spraque Atoms except the bias cap which was a 47uf/100V Xicon. All PF caps are silver mica. Mallorys in the tone and power section and Orange Drops everywhere else. The board material I purchased from Watts Tube Audio. I'm gonna do it like Leo did putting the board close to the chassis with an insulating board underneath. I'll draw up a template prior to drilling the board. I have a PT I lifted from a Silvertone amp that powered a 5AR4, 5 12ax7s, a SE EL-84 and a PP 6v6 amp (got it from ebay). It's pretty hefty looking though I know neither the make or the ratings. I have to purchase a deluxe style OT. I'm gonna start with the board and go from there. I'm really looking forward to this....

[Casey4s]

Do you know what the voltages are on the pt?

[frankeg]

Do you know what the voltages are on the pt? No not yet. I need to wait until I'm off night shift to set-up and test the transformer. I suspect it will be very close to what I need.