trinityamps.com

Got my Tramp working, and all voltages are very close to those listed in the instructions for use with a 6V6 output tube.
I removed the VRM circuit for this build and the MV is always dimed.

Are there any available voltage charts published for Tramps using 6L6, EL34, or other higher power tubes? The amp sounds only slightly louder using a 6L6 or EL34 than with a 6V6 even though wattage should be higher with the bigger bottles. I'm using the 2.5K OT tap w/EL34 & 5.0K w/6L6 tubes and check for correct bias after swapping tubes.

Would there be any possible benefit to running a higher plate voltage on the bigger tubes? I checked a few production SE 6L6 amps (Champ 12, Epiphone) and they run 6L6 plate voltages up around 450. I was considering reducing the value of the 100 ohm resistor to see if increasing plate voltage increases power/pushes the bigger output tubes harder.

The amp sounds great with 6V6's but a little weak with bigger botttles. I'd like to tweak it for use with an EL34 and only run EL34 tubes afterwards. Any ideas about the plate voltage or any other ideas to get the EL34 pushed hard?

Thanks - Tom

Have you measured the cathode resistor, what is it for the 6L6 setting? Your going to have to take the resistors out of the circuit as the bypass cap will charge up as you measure the cathode resistor with your DMM.

If your not going to be using the VRM you can remove the 100R 5W resistor (short it out).


The Tramp was designed to run at around 400V. As such the amp works optimally at that voltage level. You can try higher but that isn't going to solve your problem. You might get a bit more headroom but it won't go anything really for output levels or such.

Can you post your 6L6/EL34 voltage levels? Some pics of the amp might help too.
Don't rule out a bad tube, preamp or power.

_________________
http://pdfelectronics.com

That's normal for any kind of amp. Due to the logarithmic way we perceive loudness, you have to increase power by a factor of 10 to hear double the loudness. So you need 50W to sound twice as loud as 5W. You should however notice an increase in the amp's clean range.


Certainly try it if you like, but you won't hear a noticable difference in volume levels. However, you will have to bias the tubes colder to stay within maximum power dissipation limit, so you may just end up with harsher tone. BTW how are you measuring for correct bias?


What, weaker with the big bottles than a 6V6?? If so, this would suggest a fault in the amp.


You already have it about as close to optimum as you're going to get.

_________________
Great tones come in small glass jars!

Tom,

Here's a cut paste from my build thread regarding measurements I took with a JJ 6L6GC installed. it might help you for some reference numbers anyway.



"For other builders reference here's some voltages I measured today with a JJ 6L6GC tube fitted.
I also did the calculations to check the dissipation, which turned out to be perfect.

B+ at C12 (VRM set at Max) = 400 Volts

Measured resistance of Cathode resistors (switch in 6L6 position) = 321 Ohms
6L6 pin voltages:
Pin 3 = 393 VDC
Pin 4 = 390 VDC
Pin 8 = 27 VDC

Voltage across 1k screen resistor = 3.48 Volts
Measured resistance of screen resistor = 987 Ohms

I obtained the following values:
Voltage across Cathode resistors (27 volts) / Measured resistance (321 Ohms) = 0.084 Amps (Cathode Current)
Voltage across screen resistor (3.48 volts) / Measured resistance (987 Ohms) = .0035 Amps (Screen Current)
Subtract .0035 (Screen Current) from 0.084 (Cathode Current) = .0805 Amps (Plate Currrent)
Pin 3 to Pin 8 voltage = 365 volts

Calclating the dissipation:
Pin 3 to Pin 8 voltage (365 volts) X Plate Current (.0805 Amps) = 29.4 watts dissipation


For a Cathode Biased amp this puts me right where I need to be for the JJ 6L6GC tube's published 100% dissipation of 30 Watts

Hopefully those numbers will provide some ballpark reference to other builders when using a 6L6GC

Snowy"


Tom, if it's more volume you're after, another tip, I also found that especially in "Tweed" mode the Tramp would willingly take a very large clean boosted signal and still stay clean until around 5 on the Volume (With Master Vol dimed) but the amp is seriously louder (like a lot!). My favourite pedal to do this is the Fulltone Fatboost:
http://www.fulltone.com/products/fat-boost-fb-3
This technique makes my Tramp Head sound massive when playing with my band using a 1x12" Speaker Cab (I also added another 12" speaker cab the other night, running in parallel out of the Tramp's second speaker jack and set the Impedance switch to 4 Ohms - sounded like a lot more than a little 2 tube amp!). You can also do this in Tude mode but with a lower boosted level before encountering breakup, as the Tude already has a significant higher level of gain in the front end. If you have a clean Boost pedal handy, give it a try.


Snowy

Snowy/Kurlives/Zaphod

Thanks for the helpful & intelligent commentary.

I removed the 100 ohm resistor (thanks - kurtlives), and was able to cleanup a lot of the wiring (the VRM was also removed earlier in the build).

I wasn't expecting a significant volume increase with the big octals, just a barely noticeable one (I'm aware of the 3dB difference in human hearing & perceived volume). I also chose the wrong term 'weak sounding'. I think 'thin sounding' would have been more accurate and the Fat pull switch worked well here to correct it.

I've decided the amp is finished at this point although I may experiment with preamp cathode resistor & cap values just out of curiosity. The amp is incredibly quiet.

Along with removing the VRM circuit, I removed the 6L6/6V6 Bias switch and replaced it with a 1K linear pot in series with a 270 ohm 5 watt resistor since I would be experimenting with different brands of different tubes. I did bias readings with a SwampAMP probe (inserts between the tube and socket and connects to your meter's milliamp setting).

Here are some of the voltages I measured with different tubes installed and at the bias listed for each output tube:

6V6GT with bias set to 33 mA
Pin 3 - 411 Pin 8 - 29 C13 & C12 - 410
Red-Red diodes 630 VAC

EL34 with bias set to 57 mA
Pin 3 - 409 Pin 8 - 27 C13 & C12 - 394
Red-Red diodes 640 VAC

6L6GC (not 6LGWGB) with bias set to 69 mA
Pin 3 - 390 Pin 8 - 28 C13 & C12 - 405
Red-Red diodes 625 VAC

5881 with bias set to 59 mA
Pin 3 - 395 Pin 8 - 31 C13 & C12 - 405
Red-Red diodes 645 VAC

All preamp tube voltages were in the same ranges listed in the manual's chart for a 6V6. No surprises.

In a different post I mentioned that I burnt out the stock 6 position impedance switch and replaced it with a Marshall style 3 position switch plus a separate 2.5/5.0 switch for the OT. This cleaned up the wiring around the impedance switch.

FYI - check out the following links for fast bias calculations. Just plug in tube type and voltage and the bias is calculated:

http://www.webervst.com/tubes1/calcbias.htm
http://www.james-gang.org/jca/Bias.php

Thanks again and I'll get out some pics soon.
Tom/vdclemma

Something is still wrong most likely.

The amp should not be thin or weak regardless of the tube type used. Also when using a big octal you should notice an increase in volume/output as the difference between 6V6 and 6L6/EL34 is more than 3dB.

If you can post some pics, that will help. Since your voltages are fine it’s most likely something along the signal path.

Also unless the pot you put in series with the output tube’s cathode resistor is of sufficient power rating it is going to burn up and cause lots of problems.

_________________
http://pdfelectronics.com

Realistically, you will get around 6W out of an SE 6V6 and 11W out of an EL34 or 6L6GC. But there's absolutely no way any of them should sound thin or weak. We have pro musicians use Tramps as their stage amps, which would never be the case if there was any thinness in the tone.

_________________
Great tones come in small glass jars!