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Old 24th May 2012, 07:19 PM   #91
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I took a closer look to the schematic. IMHO there are some oddities, both on original from
Integrated5050
and the one modified and built by yurgs.

1) What is the reason of paralleling 2 triodes of the input pre-driver? I see none whatsoever. Additionally, in the original amp pre-driver have 2.5mA anode current, and yurgs' - 5mA (according to his schematic, 10mA / 2 = 5 mA).

2) Paralleling triodes in LTP - another unnecessary complexity.

3) CCS (constant current sink, MJE340) in LTP - really odd connection. Tail of the LTP doesn't seem to be connected to the ground anywhere. Emitter of MJE340 must be grounded, instead, it is connected to -87V BIAS supply. I think this is an error on the drawing (from Turneraudio).
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Old 24th May 2012, 08:05 PM   #92
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post 89 Yurg

Don't go spending into KT90's if the amp is not behaving properly; Currently your amp isn't stable. With these highish gm tubes, UL screen taps to anode R/C's is a must otherwise one can do damage.

Once stable, with KT90's fitted, expect around 20% more output power compared to KT88's. EH KT90's like more current on the UL screens and perform best with a lowish imped G1 drive. If one is after long life then OK; 475V is an easy voltage for these tubes.

richy
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Old 24th May 2012, 09:16 PM   #93
12E1 is offline 12E1  United Kingdom
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Quote:
Originally Posted by LinuksGuru View Post
3) CCS (constant current sink, MJE340) in LTP - really odd connection. Tail of the LTP doesn't seem to be connected to the ground anywhere. Emitter of MJE340 must be grounded, instead, it is connected to -87V BIAS supply. I think this is an error on the drawing (from Turneraudio).
The circuit seems perfectly OK to me. If the CCS was returned to ground then there would be very little voltage developed across it to ensure correct operation, and the other input (currently -24V) would of course need to be changed.

The current sink as drawn will work fine so long as the -87V and -24V rails are clean and the two rails are referenced to the signal ground (not to chassis). The current level is of course defined by the voltage developed across the 5.3K resistor (about 62 volts) which results in 11.7mA (hence nominally 6mA either side of the LTP).

Last edited by 12E1; 24th May 2012 at 09:28 PM.
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Old 25th May 2012, 09:37 AM   #94
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Quote:
Originally Posted by LinuksGuru View Post
I took a closer look to the schematic. IMHO there

1) What is the reason of paralleling 2 triodes of the input pre-driver? I see none whatsoever. Additionally, in the original amp pre-driver have 2.5mA anode current, and yurgs' - 5mA (according to his schematic, 10mA / 2 = 5 mA).
2) Paralleling triodes in LTP - another unnecessary complexity.
3) CCS (constant current sink, MJE340) in LTP - really odd connection. .
1.the main reason is to reduce noise, the original circuit runs 6cg7 and in my amp its 5814A, which have less gain. therefore are set at 5mA each.
3. Works fine, at least in regards to current.

@Richy, i never had anything else than KT90s and they were cheap when i bought them a while ago..
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@Audio Asylum: your paralleled Bias resistors = 666.6r
is there some improvement in sonics when using satanic valued resistors?
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Old 7th June 2012, 01:58 PM   #95
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Once (a long time ago) I paralleled some valves and forgot to use grid stopper resistors. The amplifier was an instant motorboat... bububububububububub!

Addition of 300 to 1k Ohm grid stoppers on the paralleled sections fixed it immediately.

Look at V3 and V4 in the schematic posted just recently.

Ian
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Old 7th June 2012, 02:09 PM   #96
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Looking at the earliest schematic in this post, is a separate R10 resistor used for each grid or did you tie the grids together and use a single R10?

If not, please use a separate R10 resistor for each grid and tell me if this solves it.

Ian

Last edited by soulmerchant; 7th June 2012 at 02:27 PM. Reason: blablablabla....
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Old 13th June 2012, 08:52 PM   #97
tomchr is offline tomchr  United States
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So... Yurgs. Did you get your motor boating (or whatever it was) issue solved?

~Tom
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Old 21st June 2012, 06:47 AM   #98
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Hey there, sorry for the time it takes to get back to you guys.
I am away from home for work reasons, and that will unfortunately take until the end of July. so no amp work for me :-( i managed to get the parts for my blown sound card interface, at least i am able to measure again.
i will test with a 4ohm load first and then try the gridstoppers,
yurgs
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@Audio Asylum: your paralleled Bias resistors = 666.6r
is there some improvement in sonics when using satanic valued resistors?
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Old 25th January 2013, 07:47 AM   #99
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hey there.
sometimes life gets in the way of things....
I was not able to put much time towards the amp project, but i should be able to deal with things now.

1. i changed the load to 4r, with no change in the squeeging.
2. i took out the ccs on v1 and v2, and used resistive anode-loads and i replaced the 5814 with e12AU7,
so the circuit is basically as it was designed originally, the problems stayed the same though.
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@Audio Asylum: your paralleled Bias resistors = 666.6r
is there some improvement in sonics when using satanic valued resistors?
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Old 25th January 2013, 08:22 AM   #100
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3. i checked the source,
the cleanest source i have is a pc with a soundcard 192khz
pic 7496 shows two traces of 10kHz, top=source, bottom= ampoutput at 1W
pic 7497 shows the same @ Timebase 10uS
the spikes on the top trace must be the 192kHz, and the botom trace shows the "swinging" of the trace, i hope the photo shows it a bit.
7496,10kHz_src_ampout.jpg

7497,10kHz_src_ampout10uS.jpg

4. i disconnected the driver at c26, and measured with the oscilloscope, and it looks like the trace doesn't change
pic 7499 shows two traces of 10kHz, top=source, bottom= V2 -output
pic 7500 is the same at a timebase of 2uS
there are still the lines "bluring" the trace on the output of v2. (the problem must be caused in V1/V2, the sound of the squeeging disapears though, it's made audible by the output tubes, )

7499,10kHz_src_v2.jpg

7500,10kHz_src_v2_2uS.jpg
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is there some improvement in sonics when using satanic valued resistors?
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