Advise for Nate on building his DIY Princeton Reverb

[CordovaNate]

Hi all,

My first amp!  I didn't intend to get into building an amp, but I suckered myself into buying a pulled PRRI PCB on Ebay.  Didn't work out, but by then I had so much $$$ into it I decided to go all in with the Hoff Man and do a hand wired PR...so it's all his fault!

I've never used Google photo albums, I hope this works. https://goo.gl/photos/bWWouxCUBKVYepLHA I intend to document my build as I stumble along. I know nothing, so I'm simply trying to follow instruction as best I can.

The question I have for today...the buss wire running along the back of the pots, opposite the input jacks.  Does it go to ground?  The PR layout providedhttp://el34world.com/Hoffman/files/Hoffman_PrincetonReverb.pdf seems to me to indicate that it does, but what images I can find on the internet generally don't show it grounded that way.  I've attached an image(I hope).

Thanks,

Nate

[sluckey]

The question I have for today...the buss wire running along the back of the pots, opposite the input jacks.  Does it go to ground?

Yes it does. But it's a better idea to connect that buss wire to ground at the input jacks or to a chassis ground lug near the input jacks.

[vibrolax]

Hi all,

My first amp!  I didn't intend to get into building an amp, but I suckered myself into buying a pulled PRRI PCB on Ebay.  Didn't work out, but by then I had so much $$$ into it I decided to go all in with the Hoff Man and do a hand wired PR...so it's all his fault!

I've never used Google photo albums, I hope this works. https://goo.gl/photos/bWWouxCUBKVYepLHA I intend to document my build as I stumble along. I know nothing, so I'm simply trying to follow instruction as best I can.

The question I have for today...the buss wire running along the back of the pots, opposite the input jacks.  Does it go to ground?  The PR layout providedhttp://el34world.com/Hoffman/files/Hoffman_PrincetonReverb.pdf seems to me to indicate that it does, but what images I can find on the internet generally don't show it grounded that way.  I've attached an image(I hope).

Thanks,

Nate

1) Your google photo album was perfectly accessible
2) As Slukey suggested, and as the pdf shows, the buss wire across the back of the pots connects to the ground lug of the input jack.  Some folks don't rely on the jack ring to form a chassis ground, and use a separate bolt+lug near the input jacks.   This is standard when you use isolated e.g. Cliff-style, jacks.
3) Looks pretty good so far

[CordovaNate]

So, as the ground buss is in contact with the chassis through the input jacks, I can just clip off the buss wire at the last pot?

I now understand what I did was not the best method, but it's tight in that corner where the input jacks are and my solder work is already pretty sloppy there.  I'd hate to have to get back in there.

Thanks for your advise!

[CordovaNate]

Almost there!

Today's question
I've stopped at the 47uf/100v capacitor located below the bias pot, between the pot and the ground buss ('cause it's grounded!).  The layout shows that capacitor oriented 180 degrees opposite the other capacitors and the positive side of said cap pointed towards ground.  I trust the layout is correct, but want to verify.  There is a link to the layout in my initial post.

And I've added photo's, the good, the bad, and the redundant, to the the linked photo album.

Thanks for your help!

Nate

[sluckey]

the positive side of said cap pointed towards ground.  I trust the layout is correct, but want to verify.

The layout is correct.

[CordovaNate]

Thank you!  That was fast!

Nate

[drew]

Here's why

[CordovaNate]

Here's why

Hum, I think I have been greatly overestimated.  But Thank You!

[CordovaNate]

YAY!!! Fired up w/o problem on the second try.

1st time without the dim bulb limiter it blew the fuse, a 1 amp slo blo.  I poked around, took it out to the garage and used the compressor to blow any leftovers out of the chassis, replaced the fuse and set the bias pot right in the middle, as it was cranked all the way up (or down, idk).  Back on the limiter...OK...now without the limiter, aaannnnddddd, it worked!  Made guitar noises through it for about 20 min and it seems fine.  I did note a very mild hiss, not a hum, and only noticeable when the room was quite, certainly nothing to complain about.

So Thank You all for the help!  I will likely be back for more as I learn how to set the bias. 

Nate

[drew]

Congrats on a successful first build.  A PR isn't the easiest thing in the world for a beginner.

[CordovaNate]

Thank You Drew!  I really enjoyed the process...and the results.  I played it for about an hour last night without any problems.

Today I checked the bias and got these results;

                 V5            V6
Resistance  137.7        153.9
V Drop       -3.345       -3.782
Plate Cur.   24.3mA      24.6mA
Plate V       425           425
Plate Dis.   10.34         10.44

Rookie Mistake!!!  I'm using a GZ34 rectifier, because that is what I bought for the failed PRRI rebuild.  I saw the 5U4g noted in the schematic, but I carelessly thought that was the American designation of the GZ34.  It seems that you can use the GZ34, but I've picked up a Zenith 5U4G with supposedly near NOS test results and will leave the amp alone until I swap rectifiers and recheck the bias.

[sluckey]

There is a PR that uses 5U4 and there is a PR that uses GZ34. Both are model AA1164. I would rather have the GZ34 because of the slow warm up time and the lower filament 2A current requirement, versus 3A for the 5U4.

[pompeiisneaks]

Congrats on an outstanding looking first build, I'm on like build 6 or 7 and mine still don't look that nice! :) 

~Phil

[CordovaNate]

I had wondered if I would need to go back in to add a standby switch for the 5U4G.

Maybe if I can lower the plate current I can use the GZ34.  I looked around for 6V6GT specs and only confused myself.  I have new Tung-Sol 6V6's in there and from what I saw their max plate voltage was 315, but Electro Harmonix was 425.  The info for the Tung-Sol looked like a scan of a old spec sheet and I wondered if the new tubes could handle higher voltage.

Oh well, I'm all for more internet searchin and less carpet vacuuming and other household duties.

[CordovaNate]

Congrats on an outstanding looking first build, I'm on like build 6 or 7 and mine still don't look that nice! :) 

~Phil

Thanks Phil.

I used 20ga Teflon wire I got from Hoffman for the tube side of the board and I've got to give it the credit. It's easy to work with and doesn't take up much space.

[sluckey]

Is your PT rated for 5V@3A?

[HotBluePlates]

I had wondered if I would need to go back in to add a standby switch for the 5U4G. ...

No, you don't need a standby switch.

I had multiple black- & silver-face Princetons & Princeton Reverbs over the years.  Some using a 5U4 and some using a GZ34.  None of them had a standby switch stock (and I wasn't about to add one to a vintage amp), and none of them suffered any ill effects in the years I used them.

...  I have new Tung-Sol 6V6's in there and from what I saw their max plate voltage was 315, but Electro Harmonix was 425.  The info for the Tung-Sol looked like a scan of a old spec sheet and I wondered if the new tubes could handle higher voltage. ...

The modern "Tung Sol" is made in Russia (original Tung Sol was an American company) and sold by the same distributor that brings you the Electro Harmonix (also made in Russia, but possibly a different factory).  I doubt the two brands have materially-different ratings in actual use.

Old data sheets require some interpretation, if only because there were at least 2 systems for rating (one of which always had higher numbers for the same physical tube).  Fender often ran the 6V6 well beyond published ratings for plate voltage, apparently with a nod from the manufacturer that the tubes would last "long enough".

[CordovaNate]

Is your PT rated for 5V@3A?

Mojo 760   5V@4A

[CordovaNate]

Thanks HotBluePlate,

If it don't need it, I don't want it.

[CordovaNate]

Congrats on a successful first build.  A PR isn't the easiest thing in the world for a beginner.

Honestly, the instructions, build examples, and layouts provided by Hoffman and Sluckey made the project a success.  I just went slow, double checked my work, followed their instructions.  It's been bothering me that I had not already loudly proclaimed that it would not have been possible without their help.  And Hoffman's fantastical packaging skills! 

Nate

[CordovaNate]

Just a quick update

Replaced GZ34 with a old Zenith 5U4G (huge!), here are results

            V5                V6
Res.      138.5            154.1
Vdrop    -2.656          -2.755
Current 19.18mA        17.88mA
Voltage  402               402
Wattage 7.71              7.19

I intend to just leave it alone. 

I finished my cabinet today!  Here is the link if anyone interested https://goo.gl/photos/bWWouxCUBKVYepLHA, you'll have to scroll through the amp build pics to get to the cabinet, but they are there.

Nate