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

Kegger,
I plan on eventually building a quad parallel tube SE (mono blocks) amp using TT-21's and/or KT88's from your updated design.
I have a couple questions, if you don't mind..........:)
Is it correct you spec 10uf 450v "poly or paper in oil" For C1 in PS schematic?
What variety cap should be used for C2 and C3?
What would the spec for PS fuse @ 120v be?
Would bleeder resistors for C1, C2, C3 be installed @ what value?
camman
 
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Kegger said:
Your welcome, hopefully after building your own an sourcing parts some things are learned, my hope anyway.
(you'll learn more by doing as much as you can on your own, research, sourcing, testing, Reading)
Click to expand...
Yes....... all ready learning that xfmrs/chokes are expensive and that shipping is ridiculous. Am sure that is the easy part of the 'learning'. Have a great holiday season. :thmbsp:
 
Hello everyone!
I am a newie, but after building some guitar tube amps with success, I am planning on building one of these now based on Kegger schematic (
http://www.audiokarma.org/forums/attachment.php?attachmentid=204540&d=1270619607
)

I'll be using an ECC88 driver and want to try different KT88 & EL34 output tubes.
Want to have as well, a pentode / triode / UL switch in the output section and want to keep the pots at the input. May be try a dual pot..
I'll put a switch over 270k feeback resistor (the one from output's plate to drivers plate).

Do I need two different cathode resistors for the output tube as shown in here:
http://webpages.charter.net/porkchop/tubeamp/se_kt88-full schematic.jpg ?????

Should I change the driver's cathode resistor or plate resistor ?

Extra:
Want to have 2 or 3 RCA inputs conmutable with a rotory switch.
Want to have 2 pair of outputs with a rotary switch too.

Thanks!
 
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Here is the latest updated schematic to this version of the amp.
(don't need to change anything to run EL34, 6L6GC, KT66, KT77)

.
attachment.php

The tube # on the left side of the driver is what I prefer (NOS Mullard) :smoke:, and to the right are all rollable in there.
 

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Thanks, Kegger!
Ive noticed you replaced the 100K pot and 1M from wiper to ground
(from this schematic: http://www.audiokarma.org/forums/attachment.php?attachmentid=204540&d=1270619607)
with 3k and 120k. I want to keep the pot. Shall I replace the 3k with the 100K pot ?

As well, You put a 3k in the grid of the KT88, when before there was no one.
Whats the purpose of it ??

I have want to use triod besides UL, shall I replace the 1.2K with the 100R 2W ??

Many thanks!!!
 
I generally build my amps not needing a volume pot as I use a separate preamp
but if wanting a volume control then this is how you would implement here then.
(you want the 1meg resistor shunting the pot in case of bad wiper contact)

The resistors in the grids are called grid stoppers they are there to prevent any
possible oscillations or any RF pickup for additional noise, they won't always be
needed but there not a bad idea from an engineering standpoint.

To do Triode and UL I would hook up a switch as I've put on this schematic now.

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Hey Kegger, I have lots of questions but will ask them in more than one post, if you dont mind. ;)

1. If i want to run the KT88 in pentode, shall i connect only the 100R resistor to the B+, or I need to add another one perhaps ?

2. What application do you use for building this schematics ?

3. Do i need to adjust cathode resistor or plate resistor in the driver,
if change the ECC85 for a E88CC ? (I will use a e88cc, but never know in the future if Ill need to change it). I see in the schematic it wont be neccesary, but I just find it odd..

4. Recommended voltage for 33uf and 220uf caps ?

Thanks again!
 
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If you want to run pentode do another RC stage of 4.7k an 33uf like the driver
and add that as another switch point at the outputs.
(I might change feedback to 100k, but your driver will be running out of steam)

I just use MSpaint to manipulate previous schematics to new "versions" of them.

As to adjusting for different driver tubes, the way I have this setup those ECC85
are the highest plate resistance tubes an draw the least amount of current, that
means they will have the highest plate voltage on them because less voltage will
drop across the 39k plate load resistor, and conversely the 6DJ8/6922/E88CC will
draw the most current, so means they will have the lowest plate voltage on them
because More voltage will drop across that 39k plate load resistor then.

The range from ECC85 to 6DJ8 should be roughly 200v - 135v at the plates there.
(with the other tubes settling out somewhere in between those voltages)

For the 33uf 450v, an for the 220uf 75v is fine (can always go higher on v rating).
 
Like the schematic I upload here, Kegger ?

As well:
Output transformer: 3.5K or 5K primary ?
Coupling caps voltage, 400V or 600V ?
Do I have to tie pins 1 and 8 in the KT88 / EL34 socket ??
Which resistors should be metafilm and which ones carbon ??


Thanks!
 

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I personally don't use metal film resistors, I use carbon film, carbon comp and wirewound.
(I used your schem and updated everything needed, I think to where yes it looks correct)

Put your best resistors at the 39k plate load (maybe a kiwame or koa speer) an the 3k grids.
(carbon comp make good grid stopper resistors, carbon film still pretty good as well here to)

Yes tie pin 8 and 1 together for the outputs. And those .22uf coupling caps use your favorite.
(as said you can go higher voltage ratings on the caps)

The 39k 3w could be 2 75k 2w in parallel as well there, (which is what I use since I have them)
(you can always up the wattage ratings on any of the resistors there to)

I prefer the higher 5k primary over the 3.5k, but anything in that basic range will work just fine.

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Thanks, Kegger!!
I will use 5k OT then. UL tap is in 43% ?

Regarding the power supply, shall I use 375+375V in the secondary or 350+350 ??
I have this schematic for the PS ... shall I change something ?
 

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Yep UL tap 43% (Edcor has nice priced tranny's)
An power tranny (350 - 0 - 350), 180ma or higher.
(if wanting to use EL34, (360 - 0 - 360) as highest)

And the second cap in the supply I'd run 220-470uf.
I would also change that rectifier, and use the 5AR4.

5AR4 is a 2a 5v rectifier, as is the 5V4, the 5U4 is 3A.
 
emartine said:
Thanks, Kegger!!
I will use 5k OT then. UL tap is in 43% ?

Regarding the power supply, shall I use 375+375V in the secondary or 350+350 ??
I have this schematic for the PS ... shall I change something ?
Click to expand...

I never understood the standby switch on the B+ leg at, it's better to lift the CT of the PT.

Just my opinion.
Glenn
 
Allright then. Ill use GZ34 rectifier and 350-0-350 PT.
First PS cap should be 10uf or 40uf ?
Second cap should be 220 or 470uf ?
May be I should wait to have the PT and measure if I have exactly 350 in the secondaries ?

I forgot to ask if 100R 1W in EL34 screen should be wirewound..

Those are the questions i have by now. Thanks, Kegger!
 
vfr800fiman said:
I never understood the standby switch on the B+ leg at, it's better to lift the CT of the PT.

Just my opinion.
Glenn
Click to expand...

Good catch, somehow I didn't notice it, I saw it and the fuse together as one, DOPE!
Yah I do not like that either, I do not want to slam the amp instant high voltage there.
(so I don't like stand by switches really at all)

Which is why I suggest a 5AR4 rectifier for it's indirectly heated slow warmup properties. ;)
 
vfr800fiman said:
I never understood the standby switch on the B+ leg at, it's better to lift the CT of the PT.

Just my opinion.
Glenn
Click to expand...

You mean to lift the center from the secondaries to ground, Glenn ?
Is it better ??? Just copied how I always saw it in guitar amps.. :scratch2:
 
emartine said:
May be I should wait to have the PT and measure if I have exactly 350 in the secondaries ?
Click to expand...

Remember that the 350v spec'd will be under load (presumably 180mA) with whatever primary votage was specified. Your measurement with no load on the secondaries other than other than your meter (negligible) is going to show higher than 350.
 
emartine said:
Allright then. Ill use GZ34 rectifier and 350-0-350 PT. yep

First PS cap should be 10uf or 40uf ? 10uf
(You can "tweak" it smaller to lower voltage if needed)

Second cap should be 220 or 470uf ? yes anything between there

Maybe I should wait to have the PT and measure if I have exactly 350 in the secondaries ? not a bad idea but not "necessary"

I forgot to ask if 100R 1W in EL34 screen should be wirewound.. No CC or CF

Those are the questions i have by now. Thanks, Kegger!
Click to expand...

I put the answers in Bold..
 
emartine said:
You mean to lift the center from the secondaries to ground, Glenn ?
Is it better ??? Just copied how I always saw it in guitar amps.. :scratch2:
Click to expand...

Yeah, just put the standby switch between the CT and Ground.
I was also going to say I agree with Kegger, I don't really see the need for a standby switch on a hi-fi amp. I can see it on a guitar amp, which I do to my amps.

I used a 5U4G rectifier on my build and haven't seen any issues so far.

Glenn

[EDIT]
I also forgot to mention that I put the switch scheme between the two cathode resistors on my build because I thought the bias was a little too hot for my liking when using an EL34.
 
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