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KT88 SE Abdellah (modified by Alex Gendrano) + AK..

prelius said:
Thank you Bob!

Below is a link to Amazon for a multiple connector kit that I bought...
https://www.amazon.com/gp/product/B07F5B5LLX/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I do see the benefits of building the PSU as a separate unit. As I mentioned in the original post, I have no hum in the speakers whatsoever. In addition, the chassis is more manageable. The drawback is that now I need to make two cabinets... But still, my next build will be a 6B4G pushpull with the PSU on a separate chassis.

Cheers, Paul.
Click to expand...

Thanks!

I ended up going a wee bit overboard and just purchased a set of Harwin connectors from Mouser. :)
 
Hello BlueGlow. Saw your videos buinding this in youtube. Nice work btw. This design seems to already handle EL34. I am currently using 6CA7 in triode mode, but the thing is I am only getting 3W RMS per channel.
I was expecting near 5Wrms clean power with 6CA7 in triode mode.

My voltages are:
Pin 3 of 6CA7s: 364-366 Vdc
Pin 8 of 6CA7s: 29.7 29.8 Vdc
My sensitivity is 0.73Vrms with 6AQ8, output 3.0 to 3.2 Wrms. More than that it get clipping.
B+: 379Vdc
6AQ8 pins 1 and 6: 222Vdc and 221Vdc
6AQ8 pins 3 and 8: 2.63 and 2.66 Vdc

I dont know If my problem is in the driver or the output section.
I measured my AC signal in grids of 6CA7s to be 23.8Vrms. Seems this ok to achieve the power I expect?

Your B+ is much higher than mine, but whats your approximate AC signal amplitude at the grids of your KT88s? If they are near 23Vrms.. then my problem is in the output section.
Otherwise.. perhaps in the driver bias.

THANKS!!!
 
prelius said:
Thank you Bob!

Below is a link to Amazon for a multiple connector kit that I bought...
https://www.amazon.com/gp/product/B07F5B5LLX/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I do see the benefits of building the PSU as a separate unit. As I mentioned in the original post, I have no hum in the speakers whatsoever. In addition, the chassis is more manageable. The drawback is that now I need to make two cabinets... But still, my next build will be a 6B4G pushpull with the PSU on a separate chassis.

Cheers, Paul.
Click to expand...

Nice build. Could you describe the grounding scheme of the HV and filament supplies on the two chassis? Have you ever tried to use just one umbilical?
Regards
David
 
Thank you, David

Below is a description of my PSU.
The latest version delivers: B+ 400V@200mA; 6.3V@5A AC; +12V@1A DC for VU indicators, remote volume/source switch control, etc. The B+ rectifier is SS, and I use 5V/3A winding with a SS voltage doubler to get 12V. On the PSU chassis, I have a ground wire terminated on the chassis near the power connector. This where the ground wire from the power socket and the neg of the first PSU cap is going to. I use a bus grounding schema, not a star.

All DC voltages are delivered through a 6 pin socket (I use separate B+ for each channel (2 pins), plus 1 pin for 12V). The second (3npin) socket delivers AC heaters and the ground wire. I used 6 and 3 pin sockets because they are not interchangeable, thus eliminating the possibility of plugging B+ wire into the heater and vice versa. As I mentioned, the ground wire is delivered through a heater cable. There are two reasons for this arrangement. First, to eliminate possible AC interference over DC cables (they are long, and might act as antennae); second is to preserve the tubes from cathode stripping in case the heaters were not connected properly. If the heater cable is not plugged in, there is no B+ on the plates of the tubes.

I have not tried a single umbilical, I made a decision to use two cords for the reasons outlined above.

Cheers, Paul
 
Thanks Paul,

I think I got it. Please review my understanding of your scheme. The 6 pin socket only uses 3 pins, 2 HV B+ and one +12 v. The other socket has 3 pins 2 for 6.3vAC
And the other pin is ground. The ground on the ps chassis is connected directly to a screw and nut on the metal chassis. Is the.PS ground also connected at the same point? And the ground on the amp chassis looks like is connected directly to the ground buss. Hope I was clear. Thanks again for your help.
Regards,
David
 
Haven't seen the gear.
Generally the kt 120s use more filament current.
You should check to see if there's adequate filament current available otherwise it could cause PT to fail.
Otherwise it should work fine.
 
Oh point of interest.
You won't see additional output. They "should " likely last a little longer being how there not being pushed as hard, though I can't guarantee that.
 
emartine said:
Hello! Anyone running / has runned this design with EL34? Thanks!
Click to expand...

Yes, mine is an EL34 SE.
index.php
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This schematic was my first non-kit tube amp build, back in 2013 (I think). I started out with KT88, then experimented with fat bottle 6CA7. I didn't hear much difference between the two, so I decided to build another one with some NOS EL34EH and 6SL7's that I had.
I read that the 6SL7 really should be wired in parallel to provide enough current, so that's how I did it.
GE 5U4GB rectifier, Hammond 374BX PT and Transcendar 10H choke and 10watt OPT. No feedback.
My B+ is a bit on the low side (372VDC at the EL34 plate). SS rectification is a bit high at 418V. A GZ34 should be just about right.

I'm considering replacing the driver Rk with LED and am currently experimenting with a 470Kohm feedback resistor. I can't measure distortion, but it sounds cleaner and more hi-fi to me.
 
Gotta give credit to my reference schematic. JE-Labs and @RUmad

RUmad said:
I do. It's all over the net, so I can't see why I shouldn't post it here. JE Labs is actually Joseph Esmilla. Tom just happens to build this amp as one of the amps he builds to sell I believe. Now, the schematic I'll post, I did the power supply differently from the beginning, AND I've recently changed the tube circuit as well. Optimizing for the KT88 to run hotter, and ultralinear. If you build exactly to the schematic, you will be happy though, it sounds wonderful with many different tubes. I just needed a change. At one point it was a very popular DIY build, not sure why it isn't anymore. Good luck!View attachment 798912
Click to expand...
 
jdsalinger said:
Yes, mine is an EL34 SE.
index.php
index.php


This schematic was my first non-kit tube amp build, back in 2013 (I think). I started out with KT88, then experimented with fat bottle 6CA7. I didn't hear much difference between the two, so I decided to build another one with some NOS EL34EH and 6SL7's that I had.
I read that the 6SL7 really should be wired in parallel to provide enough current, so that's how I did it.
GE 5U4GB rectifier, Hammond 374BX PT and Transcendar 10H choke and 10watt OPT. No feedback.
My B+ is a bit on the low side (372VDC at the EL34 plate). SS rectification is a bit high at 418V. A GZ34 should be just about right.

I'm considering replacing the driver Rk with LED and am currently experimenting with a 470Kohm feedback resistor. I can't measure distortion, but it sounds cleaner and more hi-fi to me.
Click to expand...

Great. How much power do you get with 372Vdc at the plates?
I have 360VDC at 6CA7 plates, and only get 3.5Wrms per channel.
Will try to use SS rectification and change 10uF filter cap to 22uF so I can increase B+ a little bit.
 
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