Single Channel BF Specs

[fusionbear]

Hello all. I am getting ready to build my Super in a Tweed combo, but I have a question about the coupling caps values coming out of the plates after the TS recovery. Because BF's have two channels, the normal channel has a .047 and the vibrato has a .1, what should I use if I am just going to do a single Normal channel. Also, after those coupling caps, there are 220K mixers and then fed to a .001 coupling cap into the PI. Should I eliminate the resistors altogether, and if I do, do I still use a .1>.001 or .047>.001, or eliminate one coupling cap and go straight from the plate into a .1 straight into the PI.

Thanks!

[rogb]

This is a single channel layout I found when I did my AB763 build. Might be worth a look through. I decided on the 2 channels in the end and they have both been used equally.

EDIT> another I referred to

[tubeswell]

... BF's have two channels, the normal channel has a .047 and the vibrato has a .1, what should I use if I am just going to do a single Normal channel.

Your choice.

However, depending on whether, and how, you implement substitutes for the 220k 'mixing' resistors, you might want to use .047uF if you do away with the 'mixing' resistors, and .1uF if you don't.

Also, after those coupling caps, there are 220K mixers and then fed to a .001 coupling cap into the PI. Should I eliminate the resistors altogether,...

The mixing resistors not only mix the 'channels', but they form part of the AC load for the prior stages. To AC, each 'active' channel's 220k is in series with the 1M grid leak resistor and the tail resistor of the LTP, so this 220k kind of acts like a bit of a voltage divider attenuating the signal slightly. Meanwhile, also to AC, the 'passive' channels 220k is in series with the 100k plate resistor of the passive channel, the whole of which is in parallel with the active channels 220k, and 110k plate resistor, and the 1M grid load resistor and the 22k tail resistor of the LTP. This also attenuates the signal slightly.

Therefore, if you go to one channel and eliminate the 220k mixing resistors, you will have less attenuation of the signal after the TS recovery stage, and this may increase the propensity for blocking distortion in the LTP and in output stage (or it may not). If you get more blocking distortion, one remedy is smaller coupling caps. (Another is grid stoppers on the affected stage's grid(s).)

... do I still use a .1>.001 or .047>.001, or eliminate one coupling cap and go straight from the plate into a .1 straight into the PI.

If you have caps in series, the effect is smaller capacitance altogether. So if go to a single cap, you might want to go with the .001uF, unless you want more bass in the signal (but beware of blocking distortion).

[fusionbear]

Thank you! You guys are great. I have learned a lot in this forum an continue to learn. I hope to return the favor always...

[Smitty]

You might like the .1 coupling cap into a 250K (or even 100K) master volume and then .01 into the phase inverter.

[fusionbear]

It is done!!!!

I used the first schematic posted by rogb. I used diodes instead of a tube rectifier. Allen trannies. A cheap mojo chassis (it needed work before I could use it.

Here is a short synopsis:

[IMG:640:480]http://i169.photobucket.com/albums/u223 ... G_1271.jpg[/img]

[IMG:640:480]http://i169.photobucket.com/albums/u223 ... G_1273.jpg[/img]

[IMG:640:480]http://i169.photobucket.com/albums/u223 ... G_1274.jpg[/img]

[IMG:640:480]http://i169.photobucket.com/albums/u223 ... G_1290.jpg[/img]

[IMG:640:480]http://i169.photobucket.com/albums/u223 ... G_1312.jpg[/img]

[IMG:640:480]http://i169.photobucket.com/albums/u223 ... G_1320.jpg[/img]

[tubeswell]

Soundbytes?

[fusionbear]

It is a little dark, but should give a decent idea of what it sounds like:

http://www.youtube.com/watch?v=u7xALxhd ... ature=plcp

[rogb]

Nice work, well done! I would love to use those Allen transformers but he doesn't do UK voltage. I'm pretty committed now to Mercury, even with the price/hype, I have been blown away by them, plus I get great support from them.

I also have a diode option in mine, definitely helps with the clean BF sound.

If you're up for a little tweaking/experimentation, you might consider:

Putting in a LarMar type PPIMV, it sounds great on mine and really useful too. You can crank up the channel , apply some MV and just clean it up with your guitar volume, it's a pedal free option.

Try some Orange Drops in place of the Mallory caps, I had Mallory types in mine and swapped most of em em out.

Try a pot or trimmer in place of the mid resistor, allows you to have the stock scoop sound or beef it up as a "raw" control.

Put a switch on the NFB, gives you a little more aggressive tone if you feel like it.

Or hell, just leave it stock

[fusionbear]

Nice work, well done! I would love to use those Allen transformers but he doesn't do UK voltage. I'm pretty committed now to Mercury, even with the price/hype, I have been blown away by them, plus I get great support from them.

I also have a diode option in mine, definitely helps with the clean BF sound.

If you're up for a little tweaking/experimentation, you might consider:

Putting in a LarMar type PPIMV, it sounds great on mine and really useful too. You can crank up the channel , apply some MV and just clean it up with your guitar volume, it's a pedal free option.

Try some Orange Drops in place of the Mallory caps, I had Mallory types in mine and swapped most of em em out.

Try a pot or trimmer in place of the mid resistor, allows you to have the stock scoop sound or beef it up as a "raw" control.

Put a switch on the NFB, gives you a little more aggressive tone if you feel like it.

Or hell, just leave it stock

Great advice, thank you!

Just to clarify, I used Solens as coupling caps everywhere except a .047 and .001 that were Mallory's due to my supplier not having the Solen's in those values. I have Orange Drops, but wanted to experiment with the Solen's on a clean amp. They do the job really well. I put a Mid control on this amp. I built this amp as a sweet sounding clean amp and it really fulfills the job...

Oh, I almost forgot. I used a 47pf bright cap on the Vol. that is soldered in, no switch. Also, I eliminated the 270K dropping resistor to simulate the loading of the Vibrato channel. Everything else follows the circuit. I am very pleased with the amp...