In Reply to: RE: The road ahead posted by Tre' on June 24, 2012 at 12:24:00:
You're not entirely wrong here. Unfortunately, it's your emphasis on only one part of an entire design that is way over the top.The Miller Capacitance of a DHT is a very real parameter, as you state, and it must be considered, as you correctly point out.
When I build an amplifier, that design is supposed to replicate a studio recording in the best way that I can build.
ALL amplifiers are sets of compromises, and in all cases, one item in a design comprising many parts and calculations may have to be changed in one or another direction-- but not too far!-- in order to allow for another important consideration-- to NOT go ignored!
In this case, I'm not willing to give up the transparency and speed of a High-mu, low plate current driver just to satisfy a desire for the ultimate in powering Miller Effect inside a DHT, although I do consider DHT bandwidth very important, as I do slew rate.
I fully understand the truly awesome performance that comes from a high-mu, low plate current driver-- as opposed to higher-current stages which are much harder to drive themselves AND THUS SEVERELY COMPROMISE THE SIGNALS COMING INTO AN AMPLIFIER FROM MUSICAL SOURCES-- that are used to drive amplifiers..
In the case of the High-Mu driver stage, it is very important to avoid overloading its output... and I recognize that you have noted this.
Accordingly, I allow wide voltage swings with high-impedance loading on the driver stage output. Certainly, the Miller Effect of the DHT being driven is also loading this stage, but I am able to get the bandwidth I need anyhow by carefully evaluating all of the factors that impinge on it.
So, the simple calculation of the filter network that is always part of a driver stage's loading, is not the only consideration there.
In your own case, I would be cautious of overestimating Miller Effect in DHTs-- different brands are very different, and plate currents and voltages that are used in a circuit operating the DHT are also contributors to the same tube exhibiting DIFFERENT Miller Effects under different operating conditions.
Miller Effect Capacitance is NOT a numerical figure that one can simply plug into a formula-- it changes with operating conditions, and with brands of tubes.
Overall Balance is everything.
In this case, Miller Effects have been recognized, but the much larger other factors present in the circuit design have also been considered-- and kept close to THEIR optimums-- all the while still keeping in mind the limitations imposed by Miller Effect, and not going overboard on that, either.
We want ideal TOTAL loading-- of the driver stage as much as is practical so that Miller Effect-- which really isn't that bad at all-- is really the only thing left that negatively affects driver stage performance.
By using such a comprehensive, overall approach, the Miller Effect that is present here simply isn't a problem.
The final result of an entire amplifier's performance is what I'm after, and in this case I have it right where I want it.
---Dennis---
Edits: 06/24/12 06/24/12
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Follow Ups
- RE: The road ahead - tube wrangler 13:43:50 06/24/12 (41)
- Dennis ..... - drlowmu 16:16:45 06/24/12 (0)
- RE: The road ahead - Tre' 14:04:44 06/24/12 (39)
- RE: The road ahead - tube wrangler 19:11:16 06/24/12 (38)
- RE: The road ahead - danlaudionut 21:46:01 06/24/12 (1)
- RE: The road ahead - tube wrangler 22:13:10 06/24/12 (0)
- RE: The road ahead - Tre' 20:30:33 06/24/12 (35)
- There needs to be a showdown in the road...... - lektrik 21:28:03 06/24/12 (34)
- RE: There needs to be a showdown in the road...... - Ralph 11:52:13 06/25/12 (0)
- RE: There needs to be a showdown in the road...... - Tre' 21:44:32 06/24/12 (32)
- Hey Tre! - DanK tubes 13:31:56 06/26/12 (19)
- RE: Hey Tre! - Tre' 18:15:54 06/26/12 (17)
- RE: Hey Tre! - tube wrangler 20:01:41 06/27/12 (15)
- "the proper connections into circuits are in the wrong places" - Tre' 12:45:58 06/28/12 (0)
- here's what started it - GSH 10:48:57 06/28/12 (2)
- RE: here's what started it - drlowmu 11:44:27 06/28/12 (1)
- RE: here's what started it - GSH 12:55:07 06/28/12 (0)
- RE: Hey Tre! - Tre' 10:13:21 06/28/12 (4)
- RE: Hey Tre! - tube wrangler 14:20:10 06/28/12 (3)
- RE: great advice, Dennis... - deathtube 667 05:36:54 06/29/12 (1)
- RE: great advice, Dennis... - tube wrangler 08:52:03 06/29/12 (0)
- RE: Hey Tre! - Tre' 21:00:51 06/28/12 (0)
- Sound Practices Information..... - drlowmu 21:14:01 06/27/12 (5)
- RE: Sound Practices Information..... - tube wrangler 14:40:46 06/28/12 (4)
- RE: Sound Practices Information..... - GSH 16:13:56 06/28/12 (2)
- RE: Sound Practices Information..... - tube wrangler 21:08:43 06/28/12 (0)
- RE: Sound Practices Information..... - tube wrangler 19:37:58 06/28/12 (0)
- RE: Sound Practices Information..... - Tre' 15:02:16 06/28/12 (0)
- Thanks Tre! - DanK tubes 19:49:20 06/26/12 (0)
- RE: Hey Dan! - drlowmu 18:10:41 06/26/12 (0)
- RE: There needs to be a showdown in the road...... - tube wrangler 22:46:36 06/24/12 (11)
- at RMAF - GEO 20:22:18 06/25/12 (10)
- RE: at RMAF - drlowmu 21:36:40 06/25/12 (9)
- RE: at RMAF - GEO 04:38:11 06/26/12 (8)
- RE: at RMAF - mach1 16:19:02 06/26/12 (0)
- RE: at RMAF - RPMac 06:32:25 06/26/12 (6)
- RE: at RMAF - Tre' 16:40:32 06/26/12 (0)
- RE: at RMAF - GEO 15:57:24 06/26/12 (1)
- RE: at RMAF - RPMac 07:20:55 06/27/12 (0)
- RE: at RMAF - drlowmu 07:05:15 06/26/12 (2)
- RE: at RMAF - GEO 15:58:48 06/26/12 (1)
- RE: at RMAF - Ray Moth 19:00:37 07/07/12 (0)