Tweed Vibrolux 5F11 - low intensity on Tremolo

[haricros]

Hey all,
I've finished a 5F11 build that sounds great, but for some reason, the intensity of the Tremolo is really as dramatic as I was hoping for. Is this typical of this circuit, or should I be looking for something wrong in the circuit itself? The only thing different about the amp is that it's going through a 12" P12P instead of a 10" P10R.

Also, how does the tremolo of a 5F11 compare to that of a 5E9a (cathode biased)? When I listen to the sound clips on the Victoria amp website, it just blows me away. It's really swampy and hypnotic. Does anyone have sound files to compare the sounds of these two amps or to see whether or not I'm on the right track?

Cheers,
Darcy

[theunrulychef]

I built a 5F11 last year that I've unfortunately since sold. The tremolo should be nice, deep & swampy. When I first fired mine up, it was a little weak too, but once I squared away the bias setting on the power tubes, it thumped great. I also tweaked the power supply a little to get closer to the schematic voltages on my pre-amp, which also helped slightly. After re-checking the bias, I'd start at the power tubes & work towards V1 in the trem circuit with your DMM. Anything that doesn't match the schematic, take a closer look. One last thing to watch out for is cheap pots. I had a dodgy one in a 18 watt head that gave me troubles.

Hope this helps a little,
Jay in Philly

[loudthud]

Do you have a bias adjustment? The bias needs to be on the cold side to get the best sounding tremolo.

[haricros]

I've adjusted the bias, and now the plate voltage for the output tubes is around 305v. It sounds great, just a bit boxy. The tremolo is definitely more pronounced, but not quite so pronounced as my Tore-vibe unit (weber circuit). The 305v is pretty low in comparison to the schematic (330v). Is this OK or should I be bringing it back up?

Also, again, I was wondering what people thought of the differences (tremolo-wise) between the Vibrolux (5F11) and the Tremolux (5E9 and 5E9a). Any thoughts?

Cheers,
Darcy

[Bruce / Mission Amps]

The plate voltage sounds low to me anyhow... mine run about +385vdc to under 400vdc with a GZ30 (5V4 type) and the 6V6 power tubes idle current is around 23ma to 26ma each. (I just check one).
I actually think it sounds great and as good as any good sounding 5E3.
If you followed the classic 5F11 layout and parts values the vibrato should be slow to start but pretty deep and very musical since the power tube's bias is going up and down... I think that makes them sound duller and brighter while oscillation for a really nice trem effect.
What transformers and rectifier are you using?

[haricros]

I'm using a Hammond 022722 Power Transformer (290 AX) with a 5Y3 rectifier. I have installed a 10K bias pot as well. As for the OT, I'm using one of Clark Amplification's 5E3 output transformers.

[tubeswell]

Originally Posted by haricros

Also, again, I was wondering what people thought of the differences (tremolo-wise) between the Vibrolux (5F11) and the Tremolux (5E9 and 5E9a). Any thoughts?

Well I built a 5G9 last year and (once I had the right speaker sorted and few other build troubleshoots ironed out) I decided its a keeper. The trem is intensely hypnotic (but it is a fixed bias amp). In fact I love that bias-vary trem so much I'm now doing a bassman variant with a 6G16 trem

[Bruce / Mission Amps]

Originally Posted by haricros

I'm using a Hammond 022722 Power Transformer (290 AX) with a 5Y3 rectifier. I have installed a 10K bias pot as well. As for the OT, I'm using one of Clark Amplification's 5E3 output transformers.

OK all good iron.

The 5F11 is fixed bias too.

Because the plate voltage is so low with your setup now (I'd really would expect to see well over 360vdc on the plates with that PT and a stock 5Y3GT).... I'd try a different rectifier first.
Keep the bias voltage on the power tubes deep enough negative that the power tubes are idling around 9-10 watts max.
Reply for help if you do not know how to get that wattage number.

Of course I'm assuming there is nothing else wrong with the amp or wiring... it could be a bad first filter cap though...

Also, I'd try a Russian 5Y3GT (actually much more like a low current version of a 5V4 and a GZ30). I like the higher B+ voltages on mine much better then the stock setup.

[haricros]

I've been going back and forth on the 5G9 vs. the 5E9a. I love the sound of a deluxe cathode bias, but I also like the idea of the cleans associated with the 5G9's bassman-style phase inverter circuit. Does anyone know if the 5e9a has any more headroom than a 5E3? The vibrolux has tons of headroom (it doesn't break up till about 5 or 6 on the volume).

Cheers,
Darcy

[haricros]

How do you get that number (watts)? I may actually have a 5U4 around, which would be interesting to try. I'll give it a whirl.

[Bruce / Mission Amps]

Get a couple 5% 1 ohm 1/2 watt resistors.
Put one 1 ohm resistor under each of the cathode lugs on each 6V6 (lug 8).
Ground one end and connect the other to the cathode of each tube.

Fire up the amp and use your VDC meter in a low voltage setting to measure the tiny voltage drop across that new 1 ohm resistor.
That means from lug 8 to ground.
If it measures .035vdc then that means that tube is drawing exactly .035a of current. Also, .035a = 35 milliamps, which is the way many of us say that current rating.
Now measure the power tube's plate voltage with respect to ground from lug 3 of the 6V6s.
In it's basic verbal terms, if you measured 300vdc from lug 3 to ground and the 1 ohm resistor netted you .035mvdc from lug 8 to ground, then the math is simply:
300vdc X .035vdc = 10.5 watts

[haricros]

I biased it all the way to the other end of the spectrum (hotter), with the plate voltages now around 362 volts with a 5y3. With a 5V4, it was around 375 volts. In both cases, the intensity was definitely better, a lot closer to what I have with my Tore-vibe. The only real difference is that the tremolo seems to be less intense at slower speeds on the Vibrolux than on the Tore-vibe. Any thoughts on why this might be?

I guess that 362 volts in today's voltage would be roughly 330 v or 340 v in 1950's with the wall voltage being lower, correct?

I can't believe how clean the amp sounds all the way up to 6 or 7 with a telecaster. Not that this is a bad thing, just different than what I've been used to.

Thanks Bruce and others for your help on this. I'll be picking up a couple of 1 ohm 1/2 watt resisters tomorrow to figure out the wattage. Will this test work the same way with a cathode biased amp like a tweed deluxe?

Cheers,
Darcy