RE: 12bh7 substitution in pilot sa 260

Posted by Cleantimestream (A) on February 27, 2012 at 00:13:40

In Reply to: RE: 12bh7 substitution in pilot sa 260 posted by pennyford on February 26, 2012 at 18:57:32:

What Eli stated{and you are already aware of} has merit about the filament current being inadequate on the 6 volt winding. Your schemo says 6.9 amps for 6.3 volt winding, that's CLOSE to the edge being your 6CA7's {x4} are drawing down 6 amps right there, leaving .9 amps to power the 12AU7 and the two 12AX7's.

If you are truly impressed by the sound, a 'safe' {albeit inelegant} way to achieve your goal without hacking or modifying the circuit would be by using two 5R4 rectifier tubes instead of the two 5U4's. Your power transformer will run cooler than you will ever recall because the 5 volt winding is now only supplying 4 amps instead of 6.

For what it is worth, the 5R4 is one of the most rugged rectifiers I have ever used and can supply the same amount of current the 5U4 does.

because you are now running the whole circuit with approximately 17 to 23 volts less {forward voltage drop of 5U4 is 44-50 volts and forward voltage drop of 5R4 rectifier is 67 volts} the sound WILL{?} change

You could insert the two 5R4 rectifiers and listen for the change and decide from there.
The Mind has No Firewall~ U.S. Army War College.

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Follow Ups Full Thread

Topic - 12bh7 substitution in pilot sa 260 - pennyford 07:59:20 02/26/12 (14)

RE: 12bh7 substitution in pilot sa 260 - pennyford 18:23:23 03/3/12 (0)

RE: 12bh7 substitution in pilot sa 260 - Eli Duttman 18:06:38 02/27/12 (0)

RE: 12bh7 substitution in pilot sa 260 - Cleantimestream 11:06:11 02/26/12 (11)

RE: 12bh7 substitution in pilot sa 260 - pennyford 18:57:32 02/26/12 (10)

RE: 12bh7 substitution in pilot sa 260 - Cleantimestream 02/27/1200:13:40 02/27/12 (5)

RE: 12bh7 substitution in pilot sa 260 - pennyford 04:48:51 02/27/12 (4)

RE: 12bh7 substitution in pilot sa 260 - Neff 20:29:12 02/27/12 (0)

RE: 12bh7 substitution in pilot sa 260 - Tom Bavis 08:14:14 02/27/12 (2)

Rectifier substitutions in Pilot SA-260... - Interstage Tranny 14:21:38 02/27/12 (1)

RE: Rectifier substitutions in Pilot SA-260... - Eli Duttman 17:26:20 02/27/12 (0)

RE: 12bh7 substitution in pilot sa 260 - Eli Duttman 19:10:59 02/26/12 (3)

I think the answer is yes - Tre' 10:06:08 02/27/12 (2)

I think the answer is ? - Interstage Tranny 14:04:19 02/27/12 (1)

I messed up, again - Tre' 16:07:42 02/27/12 (0)

Follow Ups

RE: 12bh7 substitution in pilot sa 260 - Cleantimestream 02/27/1200:13:40 02/27/12 (5)

RE: 12bh7 substitution in pilot sa 260 - pennyford 04:48:51 02/27/12 (4)

RE: 12bh7 substitution in pilot sa 260 - Neff 20:29:12 02/27/12 (0)

RE: 12bh7 substitution in pilot sa 260 - Tom Bavis 08:14:14 02/27/12 (2)

Rectifier substitutions in Pilot SA-260... - Interstage Tranny 14:21:38 02/27/12 (1)

RE: Rectifier substitutions in Pilot SA-260... - Eli Duttman 17:26:20 02/27/12 (0)

RE: 12bh7 substitution in pilot sa 260

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