Replacing 6L6 with 6V6

[Patrick M]

I have a homebuild PP amp, build with a set of transformers from an old allied radio 30W 6L6 amp.

The amp is basically using the circuits from london power (2 channel preamp, reverb, and fixed bias). Sounds great, but I would like to lower the power so I can get the sound I like (the edge of breakup/tube compression) without shackingthe whole house. I was thinking to replace the 6L6 with 6V6, and adjus the bias accordingly, as K. O'Connor suggests in his book, but:

I have a pretty high (410V) B+ voltage. In the power supply, I use diodes for rectifiers with a 600 ohm 10W resistor. How much should I decrease the B+ voltage for safe operation with 6V6? Should I add series resitors or zeners?

Should I increase the transforner impedance by connecting the 8 ohm speaker to the 4 ohm tab, or leave it alone? I guess I can always try that, but what do you think?

I would appreciate suggestions before I start changing things (particularily when it comes to avoiding blowing up components)

[txstrat]

I don't think you would be much happier with 6V6 instead of 6L6 at least regarding the power reduction. I own a DIY 6G3 Deluxe (~20W) amp with two 6V6 and a DIY 6G11 Vibrolux (~35W) and disregarding the different sounds you can barely notice the difference in headroom.
As stated here in the forum several times: 5w is half as loud as 50w (thank you ENZO).
You might better use some of these yellowjackets (THD Electronics). But even with those the amp might be still to loud. Or build yourself a good power soak.

[Patrick M]

Maybe. I am not really looking for a huge reduction in power (I live in a farmhouse on a 5 acre property), but just start to break down a little sooner. Most say that a 6V6 will start breaking down earlier than a 6V6. After reading other posts, it look lke my best bet may be convert the amp to 5e3 type - with the cathode bias and the 6V6 tube, it may very well do just what I need.

There are many posts on the 5e3 and I may find all the answers to my questions. I already have some 6V6's, do it mostly modding and changing a few R's and C's... so added cost will not be a big issue.

I guess a DIY tube amp is like a government project - never ending

[txstrat]

OK that sounds a little different. You'll surely get an earlier break up with 6V6. Just do what KO'C proposes in his TUT. 8 ohm on the 4 ohms tap would be better but most Fender OTs can handle a 100% mismatch.

[ThermionicScott]

Cathode-biasing the 6L6's would be a good start. If that's not enough, you could try leaving off the bypass cap. An intriguing idea I haven't tried yet would be to then give each tube its own unbypassed cathode resistor (doubling the resistance, obviously).

- Scott

[tubeswell]

Hi Patrick

Have you got a 5Ar4 or 5U4 rectifier in there? If so you could downsize to a 5Y3GT, as long as your reservoir filter was under about 40uF. That would knock a few volts off the B+. Assuming the amp is already cathode biased, you shouldn't need to adjust the cathode resistor either, just plonk the 6V6s in. (If it is fixed bias that's another story) And you should probably double the OT load resistance for 6V6s (by plugging in a higher impedance speaker).

[chris shaw]

diy power soak

hi Patrick
am a complete beginner and built a deluxe reverb which was too loud so was advised from this forum to build a power soak
built the one attached , it works great-- and seems to encourage earlier breakup. It took an hour to put together!!!
chris

[Patrick M]

Just to follow-up - I did the changes (6V6) and now, my output stage is just like a 5e3. 364V at B+ and 36mA bias current per tube with a 270 ohm cathode resistor. Sounds awesome - at the levels I play at I can see what all the fuss about the 5e3 is all about.

Basically it is like having a 5e3 with a reverb and a master volume - allows me to tweak it 'just right'.

A power soak may be a possible addition if I want to play quiter ad higher drives - but I will not have to attenuate as much - which will help.

[Kagliostro]

Have you considered a PPIMV

this can be the solution

look here

https://taweber.powweb.com/store/mv_schem.jpg

or you can think to a VVR (this is more easy to do in cathode bias amps than in fixed bias amp)

or look to this link

and read all with attention

Disconnecting one output tube in a push pull amp

there look to this

http://www.el34world.com/Forum/index....0;attach=4084

Kagliostro