thanks james! i'm excited now about this Pentode-2A3 project 😀
and oh, star grounding- I love it! I've tested all my amps with a friend's Avant Garde Duo and only the 300B has audible hum about a feet away from the horns. All use AC heating 😉
and oh, star grounding- I love it! I've tested all my amps with a friend's Avant Garde Duo and only the 300B has audible hum about a feet away from the horns. All use AC heating 😉
----> James D: you mean you preferred the VR to the usual SG byapss cap?
It sounds interesting ... folks here and there reported and claimed that the screen voltage has to be flat and well regulated in order to enable a better perfomance.
Ciao
Gianluca
It sounds interesting ... folks here and there reported and claimed that the screen voltage has to be flat and well regulated in order to enable a better perfomance.
Ciao
Gianluca
pentode driver
EL84 works very well! I set mine up so the the plate can never swing to a lower voltage than the screen - about 230v on plate, 150 on the screen. I intend to cap couple the screen to the cathode at some point - just haven't gotten around to doing that one. I used a simple voltage divider to obtain the screen voltage, although a gas regulator tube would be a nice touch. I am driving a 300B, has gobs of sensitivity, and good sounding el84s are not expensive (JJs are hard to beat). This should really kick butt driving a 2a3 while avoinding the difficulty of working with either hard to source or microphonic tubes. I tried the 6sl7/2a3 combo before, could never get it to my liking, although I was not using good NOS 'l7s. It sounded (and measured) rolled off in the highs. My present 2a3 amps are all transformer coupled pp (this may be the ticket!) and an SE variant of GRankins Baby Ongaku (with cheap iron). His driver circuit is a good one, and will not be the limiting factor in your amp, although many do not liKe 12at7. Good luck!
Jim
EL84 works very well! I set mine up so the the plate can never swing to a lower voltage than the screen - about 230v on plate, 150 on the screen. I intend to cap couple the screen to the cathode at some point - just haven't gotten around to doing that one. I used a simple voltage divider to obtain the screen voltage, although a gas regulator tube would be a nice touch. I am driving a 300B, has gobs of sensitivity, and good sounding el84s are not expensive (JJs are hard to beat). This should really kick butt driving a 2a3 while avoinding the difficulty of working with either hard to source or microphonic tubes. I tried the 6sl7/2a3 combo before, could never get it to my liking, although I was not using good NOS 'l7s. It sounded (and measured) rolled off in the highs. My present 2a3 amps are all transformer coupled pp (this may be the ticket!) and an SE variant of GRankins Baby Ongaku (with cheap iron). His driver circuit is a good one, and will not be the limiting factor in your amp, although many do not liKe 12at7. Good luck!
Jim
Some interesting pentode driver reading:
http://www.pmillett.com/813_se_triode_amps.htm
http://www.pmillett.com/pentodes.htm
http://www.pmillett.com/813_se_triode_amps.htm
http://www.pmillett.com/pentodes.htm
I recently built a two stage stereo SET amp using a 1619 DH octal base pentode with 2.5 volt fil on DC heat to drive an 809 DHT in A2, 6.3 volt fil also on DC heat. I used an interstage xfmer with +9 VDC G1 bias on the 809. The 809 and 1619 driver stand in series under a 625 volt B+ supply. Power for the drivers comes through the output tubes to minimize current load on the power transformer. ~375 volts plate to cathode from 420 volt plate supply on the 809. I have 200 volt plate supply on the 1619. A bit less on the plate through the I.T. I get 3.1 watts RMS per channel, similar to a 2A3. I could not get my pair of I.T.'s to match the 1619's well as a pentode and got much, much better results at a loss of gain by triode strapping the 1619 (1k R G2 to plate). In this mode this tube is really sweet and black silent! The amp turned out well and sounds very good.
I mention this as a 1619 would give one a DH alternative to a EL84/6BQ5 as a driver for the 2A3 and it is a metal octal, basically a DH 6L6.
I mention this as a 1619 would give one a DH alternative to a EL84/6BQ5 as a driver for the 2A3 and it is a metal octal, basically a DH 6L6.
Attachments
I've found with the high Gm pentodes that the VR tube definitly helps the sound when driving DHTs.
It doesn't make a difference with low Gm ones that I can hear. I tried 6B8-G, EF86, EF184 etc. and there a cap decoupling sg to the cathode sounds as good - provided it is a good cap and the right value (usually about 3-10uF not the often seen .1uF!
James
It doesn't make a difference with low Gm ones that I can hear. I tried 6B8-G, EF86, EF184 etc. and there a cap decoupling sg to the cathode sounds as good - provided it is a good cap and the right value (usually about 3-10uF not the often seen .1uF!
James
D3a / 7788
I have a D3a or E810F => IT => 300B amp.
I have the pentode in triode mode.
Would it be better to take the pentode option ?
Would a CCS in the tail lead to better sound ?
Thanks,
Jaap
I have a D3a or E810F => IT => 300B amp.
I have the pentode in triode mode.
Would it be better to take the pentode option ?
Would a CCS in the tail lead to better sound ?
Thanks,
Jaap
I think you might have to consider the fact that the 2a3 single ended might not be a good match for your speakers..(Efficiency does not tell the whole story of a speakers drive-ability)
Traditionally the classic Klipsch speakers worked best with pushpull amplifiers..( I read that somewhere) feel free to call me an armchair critic...I have been called that before.
Bas,
Interesting comment that a push-pull amp might be better for my Klipsch speakers…
I’ll look into that. I’m in the planning stage for the next amp (next winters project).
Been looking into EL34 or KT88 types…. Seen lots of P-P designs.
Here is an update on the 6sl7 issue:
Decided to try the 6sl7 in parallel. First impression is it’s an improvement over the GC-CF configuration.
Here is what I ended up with:
330v B+
47K plate R = 205 V at the plate
680R cathode R = 1.8V at 2.78mA
If anyone can explain how the parallel setup works I would love to here it?
My understanding is that we still get about the same voltage swing but at 2 times the current?
The main benefit that the tube is operating in a zone where the curves are more linear? I.e. less distortion?
How do draw the loadline for a parallel configuration?
Interesting comment that a push-pull amp might be better for my Klipsch speakers…
I’ll look into that. I’m in the planning stage for the next amp (next winters project).
Been looking into EL34 or KT88 types…. Seen lots of P-P designs.
Here is an update on the 6sl7 issue:
Decided to try the 6sl7 in parallel. First impression is it’s an improvement over the GC-CF configuration.
Here is what I ended up with:
330v B+
47K plate R = 205 V at the plate
680R cathode R = 1.8V at 2.78mA
If anyone can explain how the parallel setup works I would love to here it?
My understanding is that we still get about the same voltage swing but at 2 times the current?
The main benefit that the tube is operating in a zone where the curves are more linear? I.e. less distortion?
How do draw the loadline for a parallel configuration?
Bas Horneman said:
Bas,
You have raised a very good point! Upon completion of my 3 watt 809 SET amp I was very pleased to discover that it mated well with my Ultor-X speaker design, my latest and the one I have commercial hopes for, but was surprised to learn that it fell flat on it's face with my original Ultor speakers which exibit similar high 90's-100 dB sensitivity. My crossovers and driver configuration, as well as number of drivers are different in both speaker designs as well as the acoustical loading imparted by the design on the drivers. There are so many factors at play that it is probably impossible to quantify them meaningfully so the best and easiest way is just to try the proposed combo and see how it sounds. Trying to predict sonic outcome is doomed to failure.
Post on the audio asylum by Paul D. Scearce on plotting a load line
Posted by Paul D. Scearce on March 22, 2002 at 10:52:01
In Reply to: Load line posted by Bas Horneman on March 22, 2002 at 03:43:34:
From Ohm's law, impedance is V/I. To add an impedance line to a tubes plot, you need to find two points on the load and draw a straight line through them.
For a resistance coupled tube, start with the B+ voltage. If the plate of the tube is at that voltage, the voltage accross the load resistor is 0. From Ohm's law, current is V/R, in this case 0 ma. So the first point is at B+ v,0 ma. You can than pick any voltage less than B+ to find your second point. Lets pick 0 volts. If 0 volts appears at the plate of the tube, the voltage accross the load is B+ volts. Using Ohm's law again, current is B+/R, and your second point is B+/Rma,0v.
For example say B+ is 200v and the load is 20kohm. Draw one point at 200v,0ma and another at 0v,200/20ma(0v,10ma in other words). Then draw a straight line through these points. That is the load line.
The process is similar for a transformer coupled tube, except now there is a fair amount of dc current flowing when the plate is at B+. Using your output stage for an example, the bias conditions are probably about 100 volts on the plate at 60ma per section. (Since grid voltage is represented as a negative number on the plots, plate voltage is read from the plate to the cathode.) So draw a point at 100v, 60ma. When the plate is at 0 volts, 100 volts would appear accross the ac load, so current will be 100v/3.2Kohm or 31.25 ma. (Two sections are used in parallel, so each section will see a load of about twice the primary impedance). Add the ac current to the bias current, and draw a second point at the resulting current along the 0volt line on your graph-about 0v,90ma. Now draw a straight line through the two points for your load line.
This line passes through the grid voltage lines of the tube, so you can tell what the plate voltage will be for any grid voltage. Bear in mind this is only an approximation, but it should give you a fair idea of how the tube will opperate.
Hope this helps
Paul
Bas, your post about the plotting the loadline is the textbook (basic) one. Does it actually tell you how to plot for a *parallel* section? I don't see that. 😕
You are right..this post can't be shown in isolation..thanks for pointing that out. I had a transformer with a primary impedance of 1.6k.
Thus when calculating the current through each section one has to double the load ...
Hi sgerus,
Two methods:
1) Just use the plate curve sheet for a single tube and double the current values on the Y-axis. This method is useful if you are looking for suitable loads by trying several loadlines. It gives direct readout of power into load, distortion, etc.
2) Just use the plate curve sheet for a single tube and double the the plate load value to draw the load line for a single tube. Po results derived from the loadline must be doubled of course, since two tubes are working in this condition. This method is useful if you are stuck with a given load value (for example, an OPT you have already).
Tom
Two methods:
1) Just use the plate curve sheet for a single tube and double the current values on the Y-axis. This method is useful if you are looking for suitable loads by trying several loadlines. It gives direct readout of power into load, distortion, etc.
2) Just use the plate curve sheet for a single tube and double the the plate load value to draw the load line for a single tube. Po results derived from the loadline must be doubled of course, since two tubes are working in this condition. This method is useful if you are stuck with a given load value (for example, an OPT you have already).
Tom
Bas Horneman said:
Bas,
Until they are available in the marketplace I won't be releasing any detailed technical descriptions. The only existing pair are the large, full-range, hi-efficiency speakers which were in my avatar until recently.
Thanks Tom,
It’s starting to make sense.
I used your 2nd method, WITH one CHANGE.
Here is the actual setup for a 6sl7:
330V b+, 47K, 205V at plate, -1.88V @ cathode, 680R =2.76mA (Parallel)
To draw the LL, I doubled the plate R, AND DOUBLED THE CATHODE R.
So the LL is from 330V@0mA to 0V @ 3.5mA
The -1.88V curve lines up with 1.38mA, (based on the 2* cathode R)
Does this sound right….. finally.
Ps back to the original question of this thread:
the 6sl7 in parrallel is a big improvement over the GC-CF I started with
It’s starting to make sense.
I used your 2nd method, WITH one CHANGE.
Here is the actual setup for a 6sl7:
330V b+, 47K, 205V at plate, -1.88V @ cathode, 680R =2.76mA (Parallel)
To draw the LL, I doubled the plate R, AND DOUBLED THE CATHODE R.
So the LL is from 330V@0mA to 0V @ 3.5mA
The -1.88V curve lines up with 1.38mA, (based on the 2* cathode R)
Does this sound right….. finally.
Ps back to the original question of this thread:
the 6sl7 in parrallel is a big improvement over the GC-CF I started with
sgerus said:
Browsing this thread and interested in the general driver discussion. But I'm not sure what you're after here. Do you mean your speakers have "horn" sounds as in talking through a megaphone? If that's the case, you may improve the amp in many ways, but I don't see how it solves that kind of problem, which is the result of reflections in the horn. Or do I just misunderstand? If the latter, nevermind.
Sheldon
hi sgerus, i just want to ask if you ever wired your 6SL7 driver as SRPP and compared it with paralleled 6SL7?
sheldon, you are right. i myself is using horns (mid horn to be exact) on my speakers. i believe some larger horns were made for movie houses and would not sound "normal" for home use, unless you have a room as big and treated as a movie house. they refer to that character as the "horny" (sic) sound. mine is not horny 😀
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