Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: LooseChange on March 30, 2011, 05:30:36 am

Title: Converted RI Princeton Reverb to Point to Point
Post by: LooseChange on March 30, 2011, 05:30:36 am

Just finished this conversion.  I used a blank fiber board from Mojo. (Not sure if I would do that again). Added a midrange on back, NFB lift, variable bias, swapped in a Mercury OT and added a choke. A few challenges were where to place the filter caps and how to ground the amp my way. The amp is super quiet and sounds really good.

My only complaint is the the reverb needs a bit of warmth... Trying all the pans in the shop. Suggestions?

Title: Re: Converted RI Princeton Reverb to Point to Point
Post by: LooseChange on March 30, 2011, 05:32:47 am

Larger cabinet with a 12" speaker and tilt back legs.

Title: Re: Converted RI Princeton Reverb to Point to Point
Post by: tubenit on March 30, 2011, 05:51:26 am

LC,

Very nicely done!  That looks great!

Have you tried a 680p, 820p or .001 into the 12AT7  instead of 500p on the reverb?

With respect, Tubenit

Title: Re: Converted RI Princeton Reverb to Point to Point
Post by: LooseChange on March 30, 2011, 06:10:40 am

A larger cap... Hmmmm. Not yet.

Title: Re: Converted RI Princeton Reverb to Point to Point
Post by: Baguette on March 30, 2011, 07:56:53 am

You could try a cap to ground at the input of the reverb recovery.
Start from .002. That's the value used on SF amps. Gives a bit more warmth and cuts down oscillations. Put a .05 or .1 for a "cavey" sound.

Title: Re: Converted RI Princeton Reverb to Point to Point
Post by: Fresh_Start on March 30, 2011, 08:37:37 am

Nice work!

I'm not positive about this, but reducing the cathode resistor on the reverb driver (twin 12AT7 triodes) might move the bias point to a warmer place.  That 2.2K resistor is the equivalent of a 4.4K for each triode - kind of a "cold" bias point.

As another alternative, the .003 coupling cap between the reverb recovery stage and the Reverb pot is another possible tweaking point.  Raise that to .01uf and see if it doesn't warm things up.  Might get boomy though.  I think I'd try tubenit's tweak on the input cap first though.

FWIW Turretboards.com seems to offer an AA1164 board in the traditional Fender layout.  There's also the Hoffman-style template here if you want to roll your own.  However, LC's grounding scheme looks more like the one I used for my PR builds.  (I copied his layout style - not the other way around :wink:)

Cheers,

Chip

Title: Re: Converted RI Princeton Reverb to Point to Point
Post by: mresistor on March 30, 2011, 11:02:07 am

Very nice work LC.  Love that cabinet too.

Title: Re: Converted RI Princeton Reverb to Point to Point
Post by: phsyconoodler on March 30, 2011, 11:24:21 am

Hmmmm....I've done a few conversions and the reverb has always been quite lush;much better than the stock amp was.Maybe recheck your component values?

I drilled a hole to mount the filter cap can just like the vintage amp had but I kind of like the caps on the board like you did it.
Bet it sounds great!

Title: Re: Converted RI Princeton Reverb to Point to Point
Post by: LooseChange on March 30, 2011, 12:02:53 pm

Quote from: phsyconoodler on March 30, 2011, 11:24:21 am

Hmmmm....I've done a few conversions and the reverb has always been quite lush;much better than the stock amp was.Maybe recheck your component values?
I drilled a hole to mount the filter cap can just like the vintage amp had but I kind of like the caps on the board like you did it.
Bet it sounds great!

I checked the values and they are exactly like the original.  I think the pan makes a big difference too.
The filter caps are connected to the end of the board on the plus side. I used a terminal strip for the minus side. I also put the preamp cap on the board in the preamp area.
Everything is isolated from the chassis and ground in one place.

Title: Re: Converted RI Princeton Reverb to Point to Point
Post by: ThermionicEngine on March 30, 2011, 11:44:47 pm

Fender is using the Korean built tanks now.  I have had to replace two in the last 2 months.  I am not certain if they modified the circuit to work with the new Belton tanks.  See if you have a Belton of Accutronics.  Anyway, I put in a NOS Accutronics pan (9AB2C1B) and all was well.  See if you have the Belton tank.  As far as lushy, you could also try a 9AB3C1B.  If you can't locate one, I'got a few stashed aside somewhere.

Title: Re: Converted RI Princeton Reverb to Point to Point
Post by: stingray_65 on March 31, 2011, 01:23:39 am

Smooth as always LC.

Ray

Title: Re: Converted RI Princeton Reverb to Point to Point
Post by: DummyLoad on March 31, 2011, 02:13:42 am

ewe dew veddy noice wok LC...   

 :smiley:

Title: Re: Converted RI Princeton Reverb to Point to Point
Post by: ThermionicEngine on March 31, 2011, 10:31:28 am

PS: the amp looks great and even better on the inside.

Larry

Title: Re: Converted RI Princeton Reverb to Point to Point
Post by: Willabe on March 31, 2011, 10:47:35 am

Yeah, very nice LC!

What brand are those light blue ceramic caps?


              Brad       :icon_biggrin:   

Title: Re: Converted RI Princeton Reverb to Point to Point
Post by: LooseChange on March 31, 2011, 04:59:21 pm

Quote from: Willabe on March 31, 2011, 10:47:35 am

Yeah, very nice LC!
What brand are those light blue ceramic caps?

Thanks.. Don't know. Get them from Antique Electronics.

Title: Re: Converted RI Princeton Reverb to Point to Point
Post by: Willabe on March 31, 2011, 06:04:10 pm

Thanks LC. They are a lot nicer looking than the plain light tan/brown caps.

             Brad       :icon_biggrin: