Cathode/Fixed bias switch for half power

[vibratoking]

IME, triode mode is softer feeling and darker...it's not my preference and I don't think it's the right way to go if you just want power reduction.

Regarding VVR removing all the sparkle or chime or whatever...that's not been my experience when using reasonable volume reduction. In fact, I hear very little change tonal change. With massive reduction, the tone suffers for many reasons, some of which have nothing to do with the amp electronics.

[Reeltarded]

I had one of the stereo Riveras with every switch ever known to man and the one that never got touched was the pent/tri. The triode mode sounded like the speakers were covered in wax and the amp lost one side of the PP.

Yeah, really turble!

[randalp3000]

Never liked it on my Z Galaxie either.

[Firestorm]

Every amp I ever put triode/pentode in eventually got converted back.

[Structo]

Yeah I never understood the whole pentode/ triode switch thing.

It changes the whole character of the amp.

If you like the sound when it is loud, maybe an attenuator or power scaling would be a better choice to make it less loud.

[M Fowler]

And I though I was alone in not using this pentode/triode switch.

[jazbo8]

It seems that no one likes the idea of the triode/pentode switch - for its tone (or the lack of it). I think that just confirms the fact that most players prefer more distortion, particularly the odd order type for the output section...

[pdf64]

Also I think that the higher output impedance (of the pentode) is a factor, as it facilitates significant interaction between amp and speaker.
Pete

[rogb]

Every amp I ever put triode/pentode in eventually got converted back.

^^^^^this^^^^

I have never liked the triode/pentode mod.

How about a nice LarMar PPIMV?

I have it on 3 amps except the Dumble where I use the Dlator.

[amplifiednation]

Well the amp is a Dumble style design so the master is excellent. I also installed a second master that feeds the PI, so we are good, I mostly just wanted to play with the feature b/c I thought a 22w 6L6 cathode biased amp would be cool as an option.

Ive been tweaking voltages and have the cathode bias plates to 430. But I've noticed that the cathode bias reduces the voltage throughout the entire amp!

The volume swing is less noticeable, but there is earlier breakup and more saturation.

The PT gets HOT! I've got two GZ34 rectifiers, 2 6L6 and 5 pre's on a stock heyboer 700v Bassman transformer. Seems ok in fixed bias though, still hotter than usual. I might need to get something custom made.

[Reeltarded]

Yikes!!!

[John_P_WI]

"Tubes down" chassis hold in a lot of heat from the tubes. IF your tube rectifiers are near the transformer they can add to the heat considerably due to the proximity. Try a small muffin fan, a 12 v dc fan run at 9 v or so is almost noiseless and still moves a lot of air. Just make sure you are not over stressing the PT due to load.

[Firestorm]

"Tubes down" chassis hold in a lot of heat from the tubes. IF your tube rectifiers are near the transformer they can add to the heat considerably due to the proximity. Try a small muffin fan, a 12 v dc fan run at 9 v or so is almost noiseless and still moves a lot of air. Just make sure you are not over stressing the PT due to load.

Love those fans. Only time I use them is if I convert 4x6L6 amps to include KT88s, so I wind up freeing some of the 6.3V winding anyway (with an aux transformer) . How much current do they want? I assume it's all to get them moving.

[John_P_WI]

Firestorm, I pulled out some notes from a few years ago when I tested a Panasonic dc brushless fan FBK-08A12H.

4v @ 47.5 ma
8v@ 91.5 ma
12v @ 139 ma

It started at 4v, but very little air flow. 8 and 9 v was decent air flow and quiet, 12 v was strong flow with noise. It is a relatively linear relationship between voltage and current.

[John_P_WI]

debug delete