Hoffman Princeton reverb build tremolo problem

[Paulycoo]

Hello everyone.
I've finished my build.
Had the amp biased at 24ma...2 6v6s.
Trem is so subtle as to sound non existent.
Changed the 1M resistor to 100k as slucky mentioned previously.
Rebiased to 16ma.
Still not very strong.
I'm going to change the cap/resistor couple to a 5mm red led as slucky advised also.
Anyone have any other help to boost the tremolo so I can put bias back to 23/25ma?
Thanks!
Paul

[sluckey]

That trem circuit is capable of producing a very nice trem effect without any modification. But you need a strong tube. Try tubes first. It's possible that you have used an incorrect component value. Visually check all components in the trem circuit to insure they are correct. And verify the cathode cap positive lead connects to the tube cathode. Also look for any possible wiring errors.

If you do use the LED be sure to connect the cathode to ground. The LED will flash at the rate of the trem speed. If the LED does not flash you probably connected it backwards. If that's the case throw it away because it will be damaged now. Replace with a new LED.

[Paulycoo]

Right will do.
Thank you very much for the help.

[tubenit]

There is some good information on tremolos in ARCHIVES here:

http://el34world.com/Forum/index.php?topic=604.0

Follow Sluckey's advise until you get it working well, then you can look at that thread for mods.

With respect, Tubenit

[tubeswell]

Yes, check the plate and cathode idle voltages in your oscillator triode (with the trem switched off) to make sure everything is in the ballpark. Possible causes could be an incorrect resistor value or bad cap in the C/R network (between the LFO plate and grid), or in the connection between the LFO plate and the intensity/depth pot, or a leaky coupling cap, or a bad tube.


Also, with typical 6V6 plate voltages in the 400-420 ballpark, PRs like the 6V6s to be idling between 18mA and 22mA, as the plate dissipation heats up when the trem kicks in. What's more, if the 6V6s are biased too warm, the LFO output swing gets overwhelmed by the 6V6 tube current.

[Ed_Chambley]

Now I just do all the stuff. I actually change r my Schematic  and layout. Reason is not me. I am fortunate  to have a lot of NIB tubes. If you insur all componenta values are correct and try more tubes,  then the changes are merited..
I half all caps., still passes all frequencies needed IMO. bias with LED and reduce the one meg.  Thing always sounds like a helicopter when intensity is full. Then I have the freedom to bias hot as I feel the amp sounds best. Then when it leaves the shop. It leaves with JJ tubes. The trem works great and the little led I put on the faceplate.


I was called a genious once for. Doing this. Nothing more than what you have been told.


Now for another truth. On a scratch build Prinston reverb these days I do not bias vary my power tubes. I will either use modified Gibson tremolo or the 5g9. I never felt good about my power variable. I like a hot tube 6v6 sound. I just completed a Deluxe Reverb and heard it last night in a great band. Tremolo wiggles vi ala gibson. Amp was breaking up great ans the tremolo sounds better to me.


The ols Vibro Champs don't sel cheap for reason. I assure you.  Please know it is your build and may not practicle to wiggle a preamp tube due to your layout. I only mention this for future food for thought.




I now have a build that is a. 5g9 with a. Switcjing tonestack and a 1 tube reverb.  The tonestack is a full blackface tmb with a raw pot. One is a switching pot that connects to the tweed stack.  It is really easy.  The amp play beaitiful cleans and get very mean and a between. The verb is very nice and will actually get into surf area. V1 is a 12ay7 cause tweeds need them., but the next input goes to v2 12ax7 and i use a ab box. Both preamp tubes run in parallel all the time. And i purposely select tubes that are not balanced. Very rich tone.

[Paulycoo]

Thank you all very much.
I've checked all the wiring, all the resistors are the correct number of ohms.
The pots are correct.
Shall I replace all the caps associated with the tremolo valve?
I've tried many tubes in v4 position with no change.
Cheers all
Paul

[bnwitt]

Paul,
Could you upload some photos of the chassis and board?

[Paulycoo]

Will do thanks !

[Paulycoo]

Hello.
Still trying to optimise my photos! Sorry. Camera does 4.8m min it seems.
Question:
Could a really bad solder connection be the source of the tremolo being weak problem?
I found a horror....a dirty turret has solder dripping all over the bare wire to the next turret.
Cheers Paul

[tubeswell]

So did you measure the voltages on the oscillator stage? What are they? (Plate, Cathode and HT supply node)

[Willabe]

I found a horror....a dirty turret has solder dripping all over the bare wire to the next turret.

That could be the problem. That's a short.

Clean that up.

[Paulycoo]

Thanks I will.

Should I measure v4 pin voltages when you say the oscillator stage?
Thank you Paul

[tubeswell]

Should I measure v4 pin voltages when you say the oscillator stage?

Yes, the triode that drives the trem wiggle. (But you need to measure the idle voltages with the trem switched off, so you will need the foot switch - if its a stock BFPR circuit).

[Paulycoo]

Ok I measured valve 4 with the amp turned on and trem turned all the way down.
I'll go and turn it off with the rca plug and retest.
Pin 1: 230/240v to 180/190v fluctuating
2: 0v
3: 2v
6: 190v
7: 2v
8: 53v
Is this data of any use?
Thank you sincerely for the help it's f'in awesome to learn from you guys!

[Paulycoo]

Hello again tubeswell!
With trem off:
Pin 1: 220v
2: 0v
3: 233v on dmm 20v setting, 2.3v on 200v dmm setting
I don't understand the above voltage.
6: 186v
7: 2.8v on 200v dmm setting
8: 52v

Thanks !!!!!!
Best regards Paul

[Paulycoo]

Photo test

[sluckey]

Why haven't you put the LED in the circuit?

How much voltage do you measure on pin 5 of each 6V6?

[Paulycoo]

I was waiting to see if the voltages gave any clue as to the issue.
You said that this amp design is well capable of producing a good tremolo.
I'd rather that my amp is stock if possible.
I Will measure the 6v6 now .
Thank you Paul

[Paulycoo]

Hi Sluckey

26.4 and 26.5 on pins 5 of the power tubes.

Cheers Paul

[sluckey]

Adjust the bias pot so you have -32V on pin 5 of the 6V6s. Does the tremolo get stronger?

[Paulycoo]

Ok!
Strange stuff here....i went to change the bias pot so pin5 would read -32..
It had changed from the last reading I gave you to just about 30.
I changed it slightly.
All good.
Trem sounds good!
So pin 5 = -26.6 with trem on 10
-29.8 with trem on 5
And -32.8 with trem on 1/off.
I don't know what happened but it's cool!
Thank you for your help!
Paul

[sluckey]

Adjust the bias pot so you have -32V on pin 5 of the 6V6s. Now measure the high voltage on pin 3 of the 6V6s. And measure the millivolts on pin 8 of the 6V6s. What have you?

[Paulycoo]

Ok.
Is that -32 with trem off or on?

[sluckey]

turn trem off

[Paulycoo]

Ok
Trem off
Both tubes -32

Pin 3 on both 6v6s = 414v
Pin 8= 17 and 16 with dmm set at 2000m

[sluckey]

Ok
Trem off
Both tubes -32

Pin 3 on both 6v6s = 414v
Pin 8= 17 and 16 with dmm set at 2000m

OK, this means your 6V6s are biased at about 50% (kinda cool) Most people like to set the bias for about 70%. Adjust the bias until you have 24mV (.024V) on pin 8. Re-measure pin 3. Multiply the voltage on pin 3 times the voltage on pin 8. The target will be about 9.8. This puts the tubes idling at 70%. (Max idle power for a 6V6 is 14 watts.)

You may have to re-tweak the bias several times to get dead on 70%. When you get the bias set to 70% check the tremolo. It may be great. Or it may be too weak. If it's too weak, you have a couple choices. Find a compromise setting between optimum bias and good tremolo. Or, use the LED mod. The LED will give you a big boost in trem strength. Then you can have your optimum bias and strong trem too!

[Paulycoo]

Thank you for your time Sir.
I really appreciate it!!!!
Best regards Paul

[Paulycoo]

Got it to 9.78ish
Trem sounds great.
Master of your craft!!!!

[sluckey]

So, the whole problem was that when you had the bias voltage at pin 5 set to -24v the tubes were biased so hot that the trem effect was smothered. Those tubes were probably not gonna last very long running that hot.

With this bias exercise I was trying to show how the tremolo strength is affected by the bias. With -24v on pin 5 the 6V6 is biased hot and the trem is weak. With -32V on pin 5 the 6V6 is biased cooler and the trem is stronger. IOW, hot bias gives weak trem and cool bias gives strong trem. So, there will usually be a compromise between your "optimum' bias and good trim.

Now back to my earlier statement, "That trem circuit is capable of producing a very nice trem effect without any modification." That's still a true statement. But sometimes you may not be able to get a good trem effect if you like to run your 6V6s very hot. The LED mod will allow you to run your 6V6s as hot as you like and still have good trem.