PR Turret board/build questions

[pryde]

Hi folks,
First post here, glad to be aboard. I am looking at building a Hoffman princeton reverb (no tremolo layout):
http://el34world.com/Hoffman/files/Hoffman_PrincetonReverb_NoTremolo.pdf

My goal is to get it into a 12x8 Hammond chassis as I have a combo cab already built to house one of these chassis. So: being there are three octals, four 9-pins, can cap, transformers, reverb driver, etc. might be too tight for this footprint. The hoffman turret board looks to be about 9.5" long so that leaves little clearance for the power transformer, etc.

Anyone built this one in a small chassis? I appreciate your thoughts.
Thanks

[sluckey]

It will definitely be tight. But I think it's doable if you use a stand-up type PT (Hammond has some good choices). I suggest cutting a piece of cardboard to the size of your chassis. Then cut some smaller pieces of cardboard to size for the transformers. Bottle caps work well for tubes and cap cans. Also cut a rectangle to the size of the turret board. Spend a lot of time shuffling these around. Don't overlook the fact that fuseholders, switches, pots, and jacks take up space too, although I don't think it will cause a problem with an 8" wide chassis. I bet you can make it fit. Post a picture of your mockup and we'll take a look.

[pryde]

It will definitely be tight. But I think it's doable if you use a stand-up type PT (Hammond has some good choices). I suggest cutting a piece of cardboard to the size of your chassis. Then cut some smaller pieces of cardboard to size for the transformers. Bottle caps work well for tubes and cap cans. Also cut a rectangle to the size of the turret board. Spend a lot of time shuffling these around. Don't overlook the fact that fuseholders, switches, pots, and jacks take up space too, although I don't think it will cause a problem with an 8" wide chassis. I bet you can make it fit. Post a picture of your mockup and we'll take a look.

Thank you. Can you tell me which stand-up hammond PT works? The only stand up I could find was a Classictone (325-0-325) but it has 5 primary taps and extra plate secondaries so I did not want all the extra wire taking up space in there. Thanks!

[eleventeen]

Forget not: That where the chassis overhangs the baffle board, you lose the 3/4" or so in terms of mounting top-side parts such as the power transformer.


If you have not done this before, I absolutely urge you to heed Sluckey's suggestion and create a mockup of your chassis using cardboard cutouts, bottle caps, whatever. I am sure we can prevent you from having half a dozen headaches and we'll be happy to do so. There is a great deal of subtle interaction between parts and we have done them before. Take this extra step and save yourself a pile of time and re-do work.

[sluckey]

Can you tell me which stand-up hammond PT works?

Hammond 272X looks about perfect.

[pryde]

Forget not: That where the chassis overhangs the baffle board, you lose the 3/4" or so in terms of mounting top-side parts such as the power transformer.


If you have not done this before, I absolutely urge you to heed Sluckey's suggestion and create a mockup of your chassis using cardboard cutouts, bottle caps, whatever. I am sure we can prevent you from having half a dozen headaches and we'll be happy to do so. There is a great deal of subtle interaction between parts and we have done them before. Take this extra step and save yourself a pile of time and re-do work.

Thanks. I have built a few amps with these hammond 12x8 chassis boxes so I am familiar with the boarder limitations.

[pryde]

Can you tell me which stand-up hammond PT works?

Hammond 272X looks about perfect.

Alright. The 272X is 310-0-310 it appears (stock is 325-0-325). Also the rectifier is 2A rated (opposed to 3A on original). Good to go despite the difference in numbers?

I what about the 273CZ? The big difference is the m/a rating is 172m/a. Is that a no-go?

THanks

[sluckey]

what about the 273CZ? ...the m/a rating is 172m/a. Is that a no-go?

Way to big.Plus it's a laydown style.

310VAC will give you 438VDC (unloaded). That will sag down when connected to a PR. Use a GZ34 (2 amps) instead of a 5U4 (3 amps). Less voltage drop, less filament current, slow warm up time. Much better rectifier IMO.

[pryde]

what about the 273CZ? ...the m/a rating is 172m/a. Is that a no-go?

Way to big.Plus it's a laydown style.

310VAC will give you 438VDC (unloaded). That will sag down when connected to a PR. Use a GZ34 (2 amps) instead of a 5U4 (3 amps). Less voltage drop, less filament current, slow warm up time. Much better rectifier IMO.

Awesome. looks like a winner for this one.

[pryde]

OK here is a mock layup of the build. It is actual size (the turret board on the print measures 9.5" long). The outer edges of the paper are 12x8".

So the footprints of the PT, OT, Reverb Driver, Can cap, and rectifier tube are the yellow cutouts. I will of course be using 3/4" stand offs to float the turret board for clearance of the PT bolts, etc.

What changes would you make in positioning of the items? Best place for rectifier and can cap, etc. My main concern is hum/noise generated in the tight space.
Thanks

 

[Willabe]

Doesn't Doug have 1 of those built in that chassis? If so I'd follow his layout.

[sluckey]

Move the OT much closer to the PT. Move the RT so it sits below V2 and V3 and rotate such that the core laminations are 90° to the OT core laminations. Be sure to rotate the PT such that the core laminations are 90° to the OT core laminations also. I would mount the rectifier tube on the same center line as the other tubes.

[pryde]

Move the OT much closer to the PT. Move the RT so it sits below V2 and V3 and rotate such that the core laminations are 90° to the OT core laminations. Be sure to rotate the PT such that the core laminations are 90° to the OT core laminations also. I would mount the rectifier tube on the same center line as the other tubes.

Thanks. Here is the revised. The PT and OT lams are 90' opposed in this configuration. The rectifier tube would be squeezed pretty close to that power tube if on center but not sure if that matters in terms of noise, etc.
Is the can cap in a decent spot then?

I would love to see Doug's build if it has been done. I will do some more searching. Thanks

[sluckey]

Cap can looks fine, lots of room to move it around if necessary. You can also use individual caps lined up between the pots and edge of the board if you prefer.

Doug's PR is built in a traditional style PR chassis. Here's the link...

     http://el34world.com/Hoffman/Princeton_Reverb_Board_Build.htm

[pryde]

Cap can looks fine, lots of room to move it around if necessary. You can also use individual caps lined up between the pots and edge of the board if you prefer.

Doug's PR is built in a traditional style PR chassis. Here's the link...

     http://el34world.com/Hoffman/Princeton_Reverb_Board_Build.htm

Thanks sluckey. I did see that one already but was wondering if a non-trem one was ever built in a small chassis? Maybe I will be the first. 

Well it appears this one is doable so I will be getting everything together and moving forward.

[sluckey]

Keep us posted.

[Willabe]

If your making that a head and not a combo, you might be able to put the rectifier tube where the cap can is?

Then move the cap can to the left, or go with individual caps lined up between the pots and edge of the board, like Sluckey said.

You could put a small vent in the front or above the rectifier tube for air flow.

[pryde]

If your making that a head and not a combo, you might be able to put the rectifier tube where the cap can is?

Then move the cap can to the left, or go with individual caps lined up between the pots and edge of the board, like Sluckey said.

You could put a small vent in the front or above the rectifier tube for air flow.

Actually the plan for this one is to be in a combo and the chassis will be oriented vertically, yes vertically. 

The combo cab is done and I am able to slide different 12x8 chassis builds into it. Currently there is a Supro-type build in there but ready to do something different so I am going to slide this PR in there. Sort of a modular setup for this cab to swap in different circuits. It also features a removable baffle for 10" or 12" speaker.

Here is a pic from the back right now with the supro 12x8 in there

[sluckey]

I think you will need to use a short reverb assembly for that cab.

[pryde]

I think you will need to use a short reverb assembly for that cab.

Yep already sourced a 8AB3C1B tank for this

[HotBluePlates]

... the chassis will be oriented vertically, yes vertically. ...

You may already kow this, but there is a particular orientation of each tube when you mount the tube itself horizontally.

Basically, look at the tube in question; look for the grid support rods which run through the mica spacers, and which support each grid. Orient those support rods so they form a vertical plane (one over the other). Before drilling the tube socket mounting holes, eyeball how the tube itself will be positioned, then orient the socket, then drill.

[pryde]

... the chassis will be oriented vertically, yes vertically. ...

You may already kow this, but there is a particular orientation of each tube when you mount the tube itself horizontally.

Basically, look at the tube in question; look for the grid support rods which run through the mica spacers, and which support each grid. Orient those support rods so they form a vertical plane (one over the other). Before drilling the tube socket mounting holes, eyeball how the tube itself will be positioned, then orient the socket, then drill.

Interesting I did not consider it an issue but will look into this

[PRR]

> particular orientation of each tube when you mount the tube itself horizontally.

I know many rectifiers (and power filament triodes) have specific instructions for horizontal use.

I have never seen it for cathode tubes like we use.

And I have seen ALL possible orientations in commercial gear, even high-abuse military/industrial stuff.

Cite?

[pryde]

Another question while I am thinking this through. What would I need to change in this circuit if I wanted to use say deluxe reverb spec transformers?

I did not see a single channel no tremolo turret board for a AB763 so maybe then the princeton circuit with deluxe spec transformers and a few tweaks in the power supply?

I also would keep the mids pot omitted to save room.

EDIT: I see the PI is different as well so probably not worth going down that rabbit hole. I will stay with the princeton this build.

[sluckey]

Another question while I am thinking this through. What would I need to change in this circuit if I wanted to use say deluxe reverb spec transformers?

Nothing. Well, maybe a small tweak to the bias range resistor.

[p2pAmps]

Another question while I am thinking this through. What would I need to change in this circuit if I wanted to use say deluxe reverb spec transformers?

Nothing. Well, maybe a small tweak to the bias range resistor.

Steve, I used a DR OT in my PR and the bias range resistor turned out to be fine...FYI

[sluckey]

Steve, I used a DR OT in my PR and the bias range resistor turned out to be fine...FYI

I would not expect to have to change bias range just to use a different OT. Probably not even for a DR PT unless you decide to use the bias tap. Then you'll need to drop that 100K bias range resistor down to about 470Ω to 1K. That's why I said 'maybe'.

[p2pAmps]

Steve, I used a DR OT in my PR and the bias range resistor turned out to be fine...FYI

I would not expect to have to change bias range just to use a different OT. Probably not even for a DR PT unless you decide to use the bias tap. Then you'll need to drop that 100K bias range resistor down to about 470Ω to 1K. That's why I said 'maybe'.

 

[Ed_Chambley]

I have a AA1164 Circuit built with Deluxe Iron to run 6v6 and 6L6 and I love the amp.  I did have a problem with way too much Bass and had to run the Bass so low I did not have any flexibility.  Changed the first Bypass to 10uf/50v and the second one to 4.7uf and the coupling caps from .1 to .047 and now I have a good range where I have a nice balanced tone with the tone pots centered.  Not saying you will have the same issue, but if you do you can tweak it out.  It now sounds great with 6v6, but I really like the 6L6 best, but it is a lot louder and getting the Tremolo to work well with 6L6's biased hot was a challenge, but it was worth it to me.

[HotBluePlates]

Cite?

M-O Valve KT66 data sheet, page 5.  You'll see the same figure on the M-O Valve KT88 sheet. However, unless you're holding a KT66/KT88 in your hand, you may not notice the pin orientation shown results in the grid support rods forming a vertical plane.

O'Connor pointed it out in some of his books, noting that if a grid sagged due to overheating it is less likely to contact an adjacent electrode. I don't know that preamp tubes would benefit as much from the orientation (maybe a slightly less chance for microphonics), but it doesn't hurt to arrange them in the same manner.

I did this with the horizontal preamp tubes on my 25L15 build, and it just so happened that the resulting position of the tube sockets made heater wiring cleaner as well (but I did that in a slightly unorthodox manner).

[p2pAmps]

There are some dang smart guys on this Hoffman forum!   

[HotBluePlates]

There are some dang smart guys on this Hoffman forum!

Well, PRR is smart; I just try to avoid saying too many dumb things...