Hello Tom!
On 21 Jan 98, Tom Scioscia wrote to Rich Lockyer:
 TS>        First, I'd like to tell you guys that the project's canceled.
 TS> That's because I'm getting a REAL Blackface Dual Showman! The exact one
 TS> that I played through and fell in love with!!! My dad said that he's 
going
 TS> to get it for me. :)
Cool.
 TS>         Besides, I have the schematic. Just looked at
 TS> it, and it has 6L6s, not 6V6s. I'd be safe, either way. The 6L6s are 
being
 TS> run at 460V on the plate and 458V on the grid. Am I to assume that this 
is
 TS> within the safe range for 6L6GCs? And I shouldn't have any problem 
popping
 TS> Ruby Tubes, Svetlana, Sovtek 6L6s
I don't have the specs for the 6L6 handy... I'll check tonight if I log on 
the web.
 TS> or maybe this mystical Golden Dragon
 TS> KT66 (if it is indeed for real).
I don't know if a KT66 is a drop-in replacement for a 6L6 or not.
 TS> Besides, what I meant about
 TS> running it a bit hot is very slightly above the norm for a pristinely
 TS> clean specific amp.
The bias sets your actual potential difference between the plate and the 
cathode.  If the potential is too high, the tube will arc internally.
 TS> But I thought that it was mainly Silverfaces that were
 TS> insane on the plate voltage. If so, I was safer (if not safe) being that 
I
 TS> was going to build to the Blackface spec.
This is true.
 TS>        Why didn't the Russians and Chinese realize this?
They know, but the tubes' published specs are ###v, so they built to meet 
those specs.  Building to exceed the published specs would increase the cost.
 TS> Aren't amplifiers
 TS> at least half, if not most, of the market for these specific tubes?
These tubes are used in amplifiers *probably* 100%... however, not all 
amplifier users desire distortion or run high plate voltages.  Many 
audiophile amps run plate voltages that could smoke the best tubes made in 
the '50s, but they are biased so "cold" to prevent distortion that it's not a 
problem.  All current guitar and bass amps run voltages which are within 
these ratings... Fender was one of the few companies that went nuts with the 
B+ level, and that represents a comparatively small portion of the market.
 TS> How
 TS> does $17.50 each for JAN GE 6V6s and $18.75 each for JAN Phillips sound? 
I
 TS> know I'm going to have 6L6s, but just wondering.
No idea... I haven't been pricing tubes lately (especially not NOS), but I 
would probably drive to Phoenix and buy from AES if I were looking for NOS 
tubes.  I trust them, and don't trust shipping tubes.  Those prices sound 
close to what Jeff paid for some tubes last year, but I don't recall if they 
were 6V6 or EL84.
 TS> them listed for. BTW, I'm not sure what the amp has in it already, but
 TS> what do you think would give me the warmest tone for preamp tubes, the
 TS> 7025, 12AX7, or 12AT7? The original schematic has all three in the
 TS> circuit, but two 7025s in the inputs, one to drive the reverb, a 12AT7
 TS> recovering the reverb, a 12AT7 as the phase inverter, and a 12AX7 in the
 TS> vibrato.
The 12AT7 is a low-gain version of the 12AX7.  The 7025 is basically a 12AX7.
 TS> Also, I would assume that the 7 diodes connected to the 340VAC
 TS> tap on the power transformer is the rectifier.
7 diodes?  It's usually 4, connected as follows:
               _____________\___\__________ To Filter
   _____  | | (             /   /     |
        ) | | (                       |
        ) | | (_______                |
        ) | | (      _|_              |
   _____) | | (       -               |
          | | (_____________\____\____|
                            /    /
Again though, I'm not familiar with Showman... I'd have to see the print.
 TS> And the 6.3VAC is a common
 TS> source to the heaters on all the power tubes?
All of the tubes.  The 12A?7 series are 12v heaters, but the heaters are 
center tapped, so you tie 6.3 to the center and each end to light the whole 
thing.
C-ya! Rich
--- GoldED 2.40
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