Is this normal? Fresh Build Princeton Reverb BFR (mojotone)

[72Blazer]

New Build ad I've got about 4 hours playing time on it.
Nice and quiet, sounds great, all features work great.
he only mod I did to the amp was to enhance the tremolo circuit (changed a .01uf cap to a .022uf and changed the 1 Meg resistor to a 330K resistor)

Observations:
1.  The Light Bulb Limiter slowly reaches a pretty good glow and pulsates in relationship to the tremolo speed/intensity
2.  The amp light jewel also pulsates in relationship to the tremolo speed/intensity

Again, as far as I can tell the amp seams to be stable.

It has a fixed cathode bias and I am wondering if this is a symptom of improper bias?
Anybody ever seen similar issues before?

Vr
Jim

[mresistor]

Are you playing the amp while connected to a light bulb limiter?  If you are, you need to take the amp off the limiter and fire it up.  Please post a schematic of the amp you have built.  A Blackface Princeton Reverb has fixed bias not cathode bias. The fixed bias voltage is applied to the grids pin 5 of the 6V6s. The cathodes pin 8 should be connected to ground although many of us use a 1 ohm 1% resistor on the cathode to ground for easily checking bias with a dvm.


Is this what you built?  https://el34world.com/charts/Schematics/files/Fender/Fender_princeton_reverb_aa1164.pdf

[72Blazer]

No I was only playing the amp through the LBL for observations

Here are some pics

Thanks

[sluckey]

What wattage bulb is in your Light Bulb Limiter?

[72Blazer]

150 Watts

[sluckey]

I'm surprised that you could even see any glow with a PR plugged into a 150W bulb (other than the initial turn on current rush).

[mresistor]

If you're not on the limiter and the indicator lamp is fluctuating in intensity like the tremolo then I would say something is wrong. That would mean the 6.3vac filament voltage is fluctuating, and if that is the case ALL the tubes have filament voltage that are fluctuating. Can you put a meter on one of the 12AX7 filaments to verify that?

[PRR]

> If you're not on the limiter and the indicator lamp is fluctuating

OOH, if he IS on the limiter then bulb throb is expected. Gain is varied for trem by running the tube(s) hotter and cooler. I would not expect much glow from two-6V6 on a 150W lamp, but that glow would swing more or less to tremulate. With solid wall power there will not be enough pilot-lamp variation to see; with lamp limiter there would be more/less at the pilot light too.

[mresistor]

Right - but he didn't say if the lamp was pulsating ON or OFF the limiter..   I assume he meant it was doing that ON the limiter..but assumptions can be wrong. I don't pay attention to the pilot lamp when I use the limiter to check a new build.

[72Blazer]

Yes I am surprised as well.  I am now not so sure that my bulb is truly a 150 watt old school bulb.  They are getting hard to find.  I dont believe the pilot lamp fluctuates when on wall power.  I will verify that.  My main concern is that the LBL is glowing when this amp is plugged in other amps I own do not trigger this behavior.

R/Jim

[sluckey]

Yes I am surprised as well.  I am now not so sure that my bulb is truly a 150 watt old school bulb.  They are getting hard to find.  I dont believe the pilot lamp fluctuates when on wall power.  I will verify that.  My main concern is that the LBL is glowing when this amp is plugged in other amps I own do not trigger this behavior.

I would be concerned too. Just how bright does that 150W bulb get? Barely glowing, half bright, full bright? The brighter it is the more concerned you should be. What size fuse is in the amp? You know, it could be that your bulb is not a 150W bulb.

Buy one of these and use it to tell exactly how much current is actually flowing...

     PZEM-061 panel meter

I have one on my variac and find it very useful.

[72Blazer]

I just ordered it-thanks.

Will it have decent instructions on how to connect to my variac?

[72Blazer]

Here is a pic of Bulb and the LBL when amp is on for 30 secs

[sluckey]

I just ordered it-thanks.

Will it have decent instructions on how to connect to my variac?

You're in luck. This should get you hooked up. Read on.

     https://el34world.com/Forum/index.php?topic=25028.0

And you can see my info condensed with only the tech info on pages 4 and 5 of my amp scrapbook...

     http://sluckeyamps.com/misc/Amp_Scrapbook.pdf

Saved the best for last. This thread at The Amp Garage deals with your same variac...

     https://ampgarage.com/forum/viewtopic.php?f=6&t=32576&p=401959&hilit=variac#p401959

[Willabe]

What is your wall acv in your country?

That bulb says 150w but 120acv.

[72Blazer]

First off-Thanks Sluckey!  Awesome info

I'm in the US

[sluckey]

Yeah, about 45 miles from me!

[sluckey]

Here's a 35W 2x6L6 amp on my 60W light bulb limiter. I like the clear appliance bulbs because they give you a better indication of how bright the filament is. And 60W is my "go to" bulb for amps under 40 watts. The bulb is barely glowing but hard to tell with my cheap phone camera. My PZEM-061 panel meter says the current draw is 0.29A. And it also measures the bulb at 59.9 watts.

And a link to the appliance bulbs. Also available in clear 15W, 25W, 40W, and 60W. Shop around and you can probably find a two-pack.

6 pack clear appliance bulbs

[72Blazer]

Got it.
That's a slick LBL

[sluckey]

You can see a better pic and description on page 1 of my amp scrapbook.

[PRR]

I thot it said "ZERO LUMENS". Squinting I see it is 2080 lumens. Is that incandescent?

Google finds: Watts: 20/135/155 watts Three Way Bulb: Yes. Product Type: Incandescent Bulb. Lumens: 120/2,080/2,200 lumens.

150 Watts for 2080 lumens, 155 Watts for 2200 lumens, is pretty near the same thing. (Hot wire is not an exact technology.) So it isn't some miracle device like CFL or LED.

The "Hungary" is because they had a BIG lamp factory, TungsRam?, and may be one of the last in the business. Obviously adept at making any voltage and power and light and life the contract calls for.

[shooter]

my iz seen zero Lumens also but they also seen the light. I started over 

[72Blazer]

So I've got the meter above ordered that was recommended.  It will be here Thursday.

Q:  Is there any way to measure current draw from this amp with old school O-scope or would I need a special type of probe for the scope?

R/
J.

[72Blazer]

Greetings,

I received meter this evening and installed it on my variac (both devices listed above) and I have some test results to post.

Using the PR amp in question/plugged into the Variac and reading the newly installed meter:

Volts = 110
Watts = 68.5
A = .68

I'm thinking the results are proving no over current situation exists?  I have done nothing to the amp since I started this thread.  I can't wrap my head around why the bulb is so bright when on the LBL? 

Thoughts here?

Thanks to Sluckey for the recommendations and all the required documentation to install the meter on my variac.
R/Jim

[sluckey]

That all looks normal. I think the amp is fine. Put a jumper across the ac convenience outlet (hot to neutral) on your LBL and plug it into your variac. The bulb will glow full brightness. What wattage does your PZEM show?

EDIT... Just to be clear, put the jumper on the convenience outlet that you would connect your amp. Don't put a jumper on the lamp base socket. You may have noticed a "Bypass" push-button switch on my LBL? It's connected across my ac outlet. It allows me to quickly see the bulb at full brightness, just as if you had just screwed the bulb into a table lamp.

[72Blazer]

Well, saying a bulb is bright proved to be very subjective on my my part...
After doing as Sluckey advised I quickly realized that what I thought was bright (LBL) with the amp plugged in was nowhere near as bright as when I jumpered per his instructions.

New meter reading with the "jumper" and a true 60 watt rated bulb:

V = 110
W = 58.0
A = .52

I'm assuming the test cases are over. 

I guess I was paranoid I had a problem with this new build when I saw the brightness slowly ramp up-but again, nowhere near as bright as "jumpered".  At least I got a cool meter installed on my variac-learned more etc. in the process

Thanks to all the pros out there.

Regards,
J

[sluckey]

Nobody uses 110VAC anymore. Set the variac to 120, or 125, or whatever is stamped on that 150W bulb.
I want to know what that Hungary made 150W bulb reads on your PMEZ.

[72Blazer]

Hey Sluckey here you go:

Set the Variac to 120 Volts with the Hungarian 150 Watt bulb in the LBL and the convenience outlet jumpered:

PMEZ reads 120 Volts, 1.37 Amps, 163.3 Watts

Edit:  Very Bright-way brighter that what I was seeing with the amp plugged in/what I was concerned about...

Vr
Jim

[sluckey]

It's all good. Enjoy your new toys.