Stereo build- Mikael Abdellah's KT88 SE amp - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 14th September 2005, 08:38 AM   #11
diyAudio Member
 
Join Date: Jan 2005
Location: Lisboa
The wire closest to the UL tap goes to the plate, so in this case, it's the red wire. The blue one is B+.
__________________
"There's something organic about a happy cloud of electrons" - Neutron Bob
  Reply With Quote
Old 14th September 2005, 12:11 PM   #12
diyAudio Member
 
porkchop61's Avatar
 
Join Date: Aug 2004
Location: Mansfield, Connecticut
Thanks!
Glenn
  Reply With Quote
Old 14th September 2005, 01:38 PM   #13
Sherman is offline Sherman  United States
diyAudio Member
 
Join Date: Feb 2004
Location: Chicago area
Default Re: Re: Re: Power supply decoupling?

Quote:
Originally posted by porkchop61


...
I always have to do this on my guitar amps.

...Guitar amps are pretty narrow frequency-wise as compared with this stuff.


Glenn,
I'm in the process of building my first guitar amp right now. A single-ended EL84 combining the P1 (output stage) and P1 Extreme (preamp stages, drive and tone stack) from the AX84 site. Since I've never built a guitar amp before I'm sort of applying what little hi-fi knowledge I have and keeping my fingers crossed!

In the schematic the B+ to both preamp stages is decoupled and so is the screen if operating in pentode mode. I'm planning on putting in a pentode/UL/triode switch so I'll put in the screen decoupling filter per the schematic.

Any suggestions on good 8" speakers? If this amp turns out OK I think I'll build one for each of my sons. One plays 99% acoustic and the other is 99% electric. I assume each would need a different driver but I don't know much about instrument speakers.
__________________
--Sherman
  Reply With Quote
Old 14th September 2005, 10:54 PM   #14
diyAudio Member
 
porkchop61's Avatar
 
Join Date: Aug 2004
Location: Mansfield, Connecticut
Default Re: Re: Re: Re: Power supply decoupling?

Quote:
Originally posted by Sherman



Glenn,
I'm in the process of building my first guitar amp right now. A single-ended EL84 combining the P1 (output stage) and P1 Extreme (preamp stages, drive and tone stack) from the AX84 site. Since I've never built a guitar amp before I'm sort of applying what little hi-fi knowledge I have and keeping my fingers crossed!

In the schematic the B+ to both preamp stages is decoupled and so is the screen if operating in pentode mode. I'm planning on putting in a pentode/UL/triode switch so I'll put in the screen decoupling filter per the schematic.

Any suggestions on good 8" speakers? If this amp turns out OK I think I'll build one for each of my sons. One plays 99% acoustic and the other is 99% electric. I assume each would need a different driver but I don't know much about instrument speakers.
Hey Sherman-

Wow, something I finally know about!
Yes, definately decouple the preamp stages as shown. This is especially true for high gain amps.

I've never built the P1, I went straight for the November as my first amp. I've also reworked a McMartin 20w (6L6 PP) with the gain stages shown on the "High Octane" amp, really awesome gain. I actually don't use any overdrive/distortion peadals on this amp as the 12AX7's sound really good with the 2 gain knobs up, and the master volume down.

As for the pentode/UL/triode switch, my November build is a rev:8 version with the ultralinear/pentode switch. I can't tell the difference myself, but YMMV.

I built my own cabinet (4X12) copy of a Marshall slant-front design. I used 4 Jensen vintage alinco from Antique Elecrtronics Supply http://www.tubesandmore.com Jensen has some really nice vintage design speakers. I also looked at Parts Express as they have an excellent selection.

I'm very happy with the sound, and the price was resonable. Of course I was after a Marshall sound, but the Celestion
Greenbacks were out of my budget.

Hey, as a side note, what speakers do you use with your SET monoblocks? I have a pair of Altec A7's in the basement that I've been holding on to for years (much to the Wife's dismay).

Glenn
  Reply With Quote
Old 15th September 2005, 02:41 AM   #15
Sherman is offline Sherman  United States
diyAudio Member
 
Join Date: Feb 2004
Location: Chicago area
Default Re: Re: Re: Re: Re: Power supply decoupling?

Quote:
Originally posted by porkchop61


...
Wow, something I finally know about!
Yes, definately decouple the preamp stages as shown. This is especially true for high gain amps.

...

Hey, as a side note, what speakers do you use with your SET monoblocks? I have a pair of Altec A7's in the basement that I've been holding on to for years (much to the Wife's dismay).

Glenn
Thanks for the guitar amp info! I'll decouple just as shown. I do need the higher gain of the preamp stages. I plugged my guitar into my SE EL84 with a single 12AU7 input/pre stage and while it sounds pretty good the volume is too low and there is no chance of getting any overdrive distortion. I'm guessing 2 stages of 12AX7 which already has a mu much higher than a 12AU7 will fix that!

I like dealing with Angela and will take a look at the speakers there. My older son has a couple of 12" 2 way PA speakers and a 4x12 slantfront cabinet so I'll get to test it with those.

I'm currently using a pair of Advent/1 speakers with the KT88 monoblocks. They are 10" 2 ways. The sound is excellent, at least to my ears. I think they are about 89db/1W/1M and go loud enough for me without distortion. I've also used them with a pair of DIY line arrays built with 4" full ranges with a simple 1uF cap crossing to the tweeters. Great midrange detail and presence but no bass punch.
__________________
--Sherman
  Reply With Quote
Old 21st September 2005, 12:10 PM   #16
diyAudio Member
 
porkchop61's Avatar
 
Join Date: Aug 2004
Location: Mansfield, Connecticut
Default Power supply questions

Hi all-
I was trying to simulate the power supply for this amplifier using Duncan's PSU software. I'm using a Hammond 193J choke (10H, 200mA) because this is a stereo unit, and I need a higher current rating.



I had a few questions about what to use for values in the software.
1.) What do I use for resistance values for the 2 capacitors?
2.) What type of load do I use on the end of the power supply?
Resistive, inductive? What values would you suggest for current if an inductive load is used? What value resistance if it's a resistive load?

Thank you for any help you can give me.
I'm still learning
Glenn

Click the image to open in full size.
  Reply With Quote
Old 21st September 2005, 12:44 PM   #17
Sherman is offline Sherman  United States
diyAudio Member
 
Join Date: Feb 2004
Location: Chicago area
Glenn,
I just used the default of 2 ohms for the caps.

For the load I set it to be a constant current (the amp is running in Class A so current should be almost constant). Add the current of your two KT88s and of the 6N1P sections to get the load. I fudged and simulated it at 5mA and 10mA over my expected current draw just to make sure I didn't overload the rectifier.

I was also told that using a stepped load with the initial load about 30% to 50% higher than the expected draw gives a more accurate simulation but I'm not the one to ask about that! I did simulate it that way though and everything worked fine.

One thing I've run into with PSUDII is that I believe it assumes a value of 115VAC for mains and my mains are at 120V (most of the time!). With my simulations, for every PS I've used it for, my resulting B+ has been higher than the simulated value. My sims for my KT88 PS came out at 399 volts. My actual B+ is 425V. Still well within tube circuit allowances.

BTW, I'm hoping the final items (some caps and a couple resistor values I didn't have) for my guitar amp project should arrive today. I'm hoping to start inhaling solder fumes later in the week!
__________________
--Sherman
  Reply With Quote
Old 21st September 2005, 01:41 PM   #18
diyAudio Member
 
porkchop61's Avatar
 
Join Date: Aug 2004
Location: Mansfield, Connecticut
Thank you for that information Sherman.
I'm going to be running the KT88's at the specified 75mA (I'm using the shematic component values), but I have a question about the 6N1P.
I see it's anode current is rated anywhere between 5.6-10.5mA. I believe you said that you were running at around 5mA on your monoblock (I'm assuming you only have one plate connected). Does this mean I should double that for a stereo version? After all, I'm using both sides of the tube. Maybe it's safer to estimate the current at the max of 10.5mA?
I'm getting close to the max current rating of the Hammond 273BX (175mA). I'd better watch the final B+ outcome, and bias accordingly

I forgot to ask, what are you using for a schematic for the guitar amps? I think you said it was part of 2 different designs?
Please post pix when you get the chassis done. I'd be intersted in seeing them.
Glenn
  Reply With Quote
Old 21st September 2005, 01:45 PM   #19
kmtang is offline kmtang  Canada
diyAudio Member
 
kmtang's Avatar
 
Join Date: Nov 2004
Location: Vancouver
Default Hammond 1627 OPT

I believe the Red wire goes to B+ and Blue wire goes to the plate. To make sure you get the best performance from the OPT, try connect it both ways and measure it's frequency response.

Johnny
Attached Images
File Type: gif 1627se_sch.gif (3.3 KB, 1113 views)
  Reply With Quote
Old 21st September 2005, 01:51 PM   #20
kmtang is offline kmtang  Canada
diyAudio Member
 
kmtang's Avatar
 
Join Date: Nov 2004
Location: Vancouver
I just noticed that Hammond's OPT has new configuration. The new version having all 4, 8, and 16 ohm tappings available. The oldere version either you can configured it to 4 and 8, or 16-0hm only.


Johnny
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Mikael Abdellah's kt88, (LOADLINES) soundbadger Tubes / Valves 6 3rd January 2012 02:30 AM
6CA7 Mikael Abdellah's KT88 SE amp? porkchop61 Tubes / Valves 24 20th February 2011 03:31 PM
Improvements for the Mikael Abdellah KT88??? 69CamaroSS396 Tubes / Valves 42 16th December 2009 01:58 AM
Mikael Abdellah SE KT88 ideas and questions kacernator Tubes / Valves 6 14th January 2008 01:09 PM
Looking for KT88 Amplifier Schematic by Mikael Abdellah jduffy Tubes / Valves 6 5th April 2007 09:02 PM


New To Site? Need Help?

All times are GMT. The time now is 02:05 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2