Hoffman Princeton Reverb Build

[sclinchy]

Just my second build, so please be gentle :).






Powered up for the first time, no tubes installed except for the rectifier (5U4).


Power light comes on.  Measured 6.3v at all of the heaters, 5v at the rectifier heaters.


Measured about 665v AC across pins 4 and 6 of the rectifier, still OK, right?


I measure DC at one of the filter caps and the chassis and bet 0.


Am i measuring that correctly?  If so, any idea what I might have done wrong there?


Layout and schematic here: http://el34world.com/Hoffman/files/Hoffman_PrincetonReverb.pdf


Thanks in advance for your patience.

[bnwitt]

Meter set to dc and standby switch is on?

[John]

Measure DC from pin 8 to ground. It's been a while since I used a tube there, but I'm thinking your meter should be going a little "whacky" if you're measuring AC across pins 2 & 8, since 8 will have (hopefully) around 400 vdc on it. Anyone else, is my thinking right?

[sclinchy]

I get 1v DC at pin 8!

[shooter]

I get 1v DC at pin 8!

standby switch open, or closed?
If closed power off, discharge caps then ohm A-D to ground, hopefully you have many, many thousand ohms at each.

[hesamadman]

You'll have a much higher voltage reading with no tubes installed. 0 volts at filter cap? There's not much to trouble shoot there. Generally B+ rail leaves rectifier and sees a resistor then filter cap. Resistor then filter cap. Is this cap that's reading 0 in line and correctly installed? are you sure you're not measuring negative side of cap to chassis?

[sclinchy]

My PT has a 50 volt bias wire.  Any idea what I ought to be doing with that?

[pompeiisneaks]

My PT has a 50 volt bias wire.  Any idea what I ought to be doing with that?

It shouldn't be needed, the schematic and layout shows a wire coming off one side of the PT secondary to the bias, it just half wave rectifies and resistor drops the voltage to where you need it for bias.  You can put shrink wrap on the end so it can't accidentally ground out and wrap it away from the rest of the amp.

Did you turn the standby switch on like asked?  Measure voltage on both sides of the standby switch do you get the 600ish volts on both sides of it?  If not it's off, and you need to turn it on to get the voltage to the other side of it (heaters and 5v bypass that).

Pictures of the amp would help too.

~Phil

[sclinchy]

Thanks again.  No standby switch, just turned power on.

[sclinchy]

And I measure 115  volts AC at the switch, which is what i’d expect, that’s just what’s coming out of the wall at that point, right?


Sorry if i’m being dense!

[pompeiisneaks]

Yes you should have 115 to 112 AC at the power switch, before it goes into the Transformer.  You say you saw 600 ish volts DC at pin 8 right?  (BTW with your multimeter you can just clamp the black lead to the chassis for ground and then connect the red end to whatever voltage you're trying to test, just be very careful to either turn it off in between switching leads or you could cause arc's or touch something yourself and shock yourself). 

You should have the same voltage at pin 8 on the rectifier as you have at the first power capacitor.  Then at each point down the line it should drop some due to the dropping resistors (10k and 22k).  If you have no voltage on any of that rail, you've got something wired wrong.  It's just the output of the rectifier. 

Again pictures of the amp will really help, just make sure they're well lit and not blurry.

~Phil

[sclinchy]

Sorry for the lack of response, work has had me travelling that last couple of weeks, just now getting back to this.


Attached is a picture, I hope it's clear enough.


Just to make sure I'm checking this correctly, I'm measuring DC voltage at pin 4 or 6 of the recto to ground, right?  I can't understand how I'm getting 0 volts there, that should be B+ straight from the PT?


Thanks again for your patience and understanding.

[sluckey]

Pin 4 and pin 6 are AC voltage. If your meter is set for DC measurments then it will read zero volts DC. Look at pin 8 to see DC volts.

[Glenn]

Hi sclinchy. You should look at your fuse connection, it looks a little burnt and the solder connection doesn't look like there is any solder there. Your meter readings might be glitchy, because of it
Good luck

[pompeiisneaks]

Yeah I agree, not only does that look like it may not have a good solder connection, I see the rectifier seems like it may need some more solder on the yellow wire on what is likely pin 8 (where there's also a red wire).  Basically, it looks like you could try and do a bit more soldering on a few of those joints to make the solder flow into it a bit better.  It wouldn't hurt to put a little flux on them as well to clean off any oxidation etc.  (that is if you don't have flux cored solder that's 5 core type, that stuff tends to always do pretty well)

~Phil

[pompeiisneaks]

Here are a few screenshots of the specific area taht I think may need a bit better soldering, with more solder in the joint.  Any other places you see like this, try and reflow some solder into the joint, don't over do it, just make sure the hole is filled well, and the solder looks nice and shiny when cooled.

~Phil

[John]

Just to make sure I'm checking this correctly, I'm measuring DC voltage at pin 4 or 6 of the recto to ground, right?  I can't understand how I'm getting 0 volts there, that should be B+ straight from the PT?

Pin 4 and pin 6 are AC voltage. If your meter is set for DC measurments then it will read zero volts DC. Look at pin 8 to see DC volts.

I think that's the real thang. Yes that fuse connection isn't right, but it's 'working" right now.

[sclinchy]

Thanks.
Resoldered the fuse holder and pin 8 on the recto, still no DC there.


I'm confused about that pin.  There is supposed to be 5v AC there for the heater (there is) and there's also supposed to be about 420v DC?

[Willabe]

Just to make sure I'm checking this correctly, I'm measuring DC voltage at pin 4 or 6 of the recto to ground, right?  I can't understand how I'm getting 0 volts there, that should be B+ straight from the PT?

Pin 4 and pin 6 are AC voltage. If your meter is set for DC measurments then it will read zero volts DC. Look at pin 8 to see DC volts.

I think that's the real thang. Yes that fuse connection isn't right, but it's 'working" right now.

Yes.

[sluckey]

I'm confused about that pin.  There is supposed to be 5v AC there for the heater (there is) and there's also supposed to be about 420v DC?

You should only measure 5VAC if you put one meter probe on pin 2 and the other probe on pin 8. There will be approx. 420VDC between pin 8 (or pin 2) and chassis ground.

[EL34]

clinchy
All your emails from the forum are bouncing back
The message says user unknown
clinchys at earthlink dot net


I removed your subscription from this post

[sclinchy]

Wow, sorry, that's very old.  Updated now.

[EL34]

Wow, sorry, that's very old.  Updated now.

Thanks
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[sclinchy]

We may have a winner.  I pulled the recto and the center post was broken.  Threw a 5Y3 that I had sitting around and now I've got 437vDC on pin 8.  Similar voltages on the filter caps!


Time to plug in some tubes after I check a few more voltages


Thanks everyone for the he!p, I'm sure I'll need more.

[jojokeo]

more bad soldering areas...

[EKDENTON]

On the terminal rings that are bolted to the chassis they look like they have been crimped rather than soldered. They may work for a time like that but eventually oxidation will deteriorate the connections and cause problems.


While your soldering some of the other spots you might consider soldering all those also.


JMHO

[sclinchy]

I did a bunch or re-soldering, as was pointed out there were some bad joints there.


I've now installed tubes, plugged in a speaker and even with the volume at 0, I get a sound like an airplane landing.  It gets louder as the tubes warm up and I have to turn the amp off.


Some sort of feedback loop?  Any suggestions as to where to start looking?


Thanks again to everyone.

[sluckey]

Disconnect the NFB wire from the speaker jack to the board. If that fixes it then swap the OT plate leads between the 6V6 sockets and reconnect the NFB wire.

[sclinchy]

Damn.  No change, except that the volume of the noise doesn’t seem to increase once the tubes are warmed up.  It’s just a very loud hum.  The volume control has no effect on it.

[purpletele]

Damn.  No change, except that the volume of the noise doesn’t seem to increase once the tubes are warmed up.  It’s just a very loud hum.  The volume control has no effect on it.

As I read through your battles it is starting to sound like possibly a polarized cap is reversed.  I am trying to think of what would cause an uncontrollable loud hum? 

I put 2 cents on a reversed cap.

[sclinchy]

Thanks, just checked all of the electrolytics, they’re all correct.  None of the others should be polarized, right?

[purpletele]

Thanks, just checked all of the electrolytics, they’re all correct.  None of the others should be polarized, right?

Are you going bonkers yet?

Wow, I bet there is something obvious, well something simple anyway.

You can check that off now.

BV

[pompeiisneaks]

If you can get some more high rez photos of the entire insides we may be able to see what else may be amiss...

~Phil

[ac427v]

I'm trying to see the colors of the power transformer leads but can't tell if I'm seeing a green wire with a white tracer stripe or green wire with a reflection on it. It looks like a green with white tracer (or reflection) goes to the heaters. And a green heater lead (no tracer) goes to a plus terminal on the cap can and then to the ground bolt. Can you tell us how the PT leads are wired?
--Craig

[sclinchy]

Tried uploading all of these at once, but they were too big.  I'll put them on separate replies.

[sclinchy]

#2

[sclinchy]

#3

[sclinchy]

And #4.


Let me know if there is anything else you'd like to see.

[Sonny ReVerb]

Maybe an angle shot of the back of the input jacks/pots?

Start here: http://www.geofex.com/ampdbug/hum.htm

Another great resource (see pg 51): http://theguitar-blog.com/wp-content/uploads/2013/06/Electric-Guitar-Amplifier-Handbook.pdf

[purpletele]

And #4.


Let me know if there is anything else you'd like to see.

Sclinchy,

These guys will need a much clearer shot with good lighting.  Include the whole chassis gut shot so we can all follow your layout and see where everything is terminated.

There is obviously something connected incorrectly so a view of the entire chassis gut will help.

In order to post multiple photos you have to open a photo in MS Paint or similar and resize the photo to the Allowable dpi size, I think I use 1280 as the value.  You need to save the photo under a new name.

There is a comprehensive set of instructions, it's quite amazing to see all of the information that Hoffman has developed and stored for us.

[pompeiisneaks]

Yeah there's a lot of darkness in those shots making it hard to see, you may also want to use some third party image hosting like imgur or google photos so you can upload them at full resolution.  See if you can get good overhead lighting.  The resolution looks good, but I can't make out some areas due to either too dark or too much direct shiny light.

~Phil

[sclinchy]

Is this better?  Not only am I a lousy solderer, I'm a bad photographer as well!

[pompeiisneaks]

MUCH better :) 

[pompeiisneaks]

Oh and a good shot of the pots and jacks and the opposite side with the rca's and output connections, those aren't quite totally visible. 

I'm not seeing anything specifically out of whack.  I'd suggest getting voltage readings on eacy of the filter capacitor pins to ensure they're getting voltage and therefore are filtering correctly.  Additionally, make sure to get voltage readings on all the important pins of every tube and post here.  That will help ensure that the tubes are around the right voltage.  Make sure you used the 40uF one for the first filter node, ( don't know from those caps for sure if that right top one is the 40uF, but make sure.)    It could be motorboating going on.

Also do some thorough testing with continuity mode to check that continuity is working through every place it should. 
The best way to do that is to go to some point before a turret, and then some point after it, don't measure right on the turret because you could be creating the connection by adding pressure on it. 

Example, test continuity on the power rail by touching the leads of the 100k resistors between two nodes, that confirms you've got continuity between those leads, through the turret and through the jumper wires you've got there. 

Check leads between resistors/capacitors and the tube pins by touching the lead of the component and the pin of the tube, not the turret, or wire itself. 

Just be super anal about making sure EVERY connection is solid and has no bad connections. 

Double check that your under board jumpers haven't somehow come undone in resoldering things, etc. 

Check grounds from leads throughout the entire grounding busses, not on the turret or buss wire itself.

I'm not seeing anything that seems missing, but just thinking of other possible areas. 

If you don't find anything, but give us the voltages it may point out a specific trouble area.

~Phil

[bnwitt]

Your 1-2 input jacks are not wired correctly.  You shouldn't have a 33kohm resistor on pin 2 of V1 unless you don't have jack #2 wired in at all.  Is that the case?  It doesn't look like there are any wires going to the #2 jack so maybe that is what you did

[bnwitt]

It doesn't appear that your reverb transformer black wire is grounded and it looks like you grounded the green wire instead.  It looks like it is going to the RCA connector's center pin instead of the green.  I guess it's ok to swap those secondary wires but for the sake of accuracy it doesn't match the layout.  Also, I don't see the 220k resistor to ground from the Reverb return RCA connector.  I only see (2) RCA jacks??  And it doesn't appear that you ran a chassis ground from the speaker jack ground pin.

[pompeiisneaks]

Your 1-2 input jacks are not wired correctly.  You shouldn't have a 33kohm resistor on pin 2 of V1 unless you don't have jack #2 wired in at all.  Is that the case?  It doesn't look like there are any wires going to the #2 jack so maybe that is what you did

Yeah I was suspicious of some of these, but that's why I asked for straight on photo's since they're kinda obscured.

~Phil

[sluckey]

Your 1-2 input jacks are not wired correctly.  You shouldn't have a 33kohm resistor on pin 2 of V1 unless you don't have jack #2 wired in at all.  Is that the case?  It doesn't look like there are any wires going to the #2 jack so maybe that is what you did

Look at Hoffman's drawing.

[bnwitt]

Your 1-2 input jacks are not wired correctly.  You shouldn't have a 33kohm resistor on pin 2 of V1 unless you don't have jack #2 wired in at all.  Is that the case?  It doesn't look like there are any wires going to the #2 jack so maybe that is what you did

Look at Hoffman's drawing.

Yes I did, but his photo shows a 1-2 input jack configuration not the single input jack of the drawing.  So that would mean jack 2 is dead.  It looks like a Mojotone chassis which has two input jacks just like the original BFPR.  Why does the Hoffman layout just show the single jack?

[sluckey]

I think he just used the second jack to plug the hole on his store bought chassis/faceplate.