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

Using VR tubes is a neat idea. I was all set to pursue it but then i read that they can add noise to a circuit. This issue or non issue i could not verify to my satisfaction. So i let the implementation for a single ended amp aside, for now. If anyone really tried it and can give their impression pro or con, i would appreciate it.

I've done it in a few of my builds... I could never hear any additional noise, and neither could people I built the amps for... Come to think of it, how would one track/measure it? I guess this is a question for a larger audience... Might be worth separating this into a separate thread...
Cheers, PZ
 
I've done it in a few of my builds... I could never hear any additional noise, and neither could people I built the amps for... Come to think of it, how would one track/measure it? I guess this is a question for a larger audience... Might be worth separating this into a separate thread...
Cheers, PZ
While the VR tubes are a neat idea they do have a lot more circuitry and parts. Tube sockets, wiring, resistors and capacitors, Not to mention, extra current required for the tube filaments. I thought when you added it all up, a SS high voltage supply seems to be a viable alternative that could be purchased complete and with .very low noise output.
 
While the VR tubes are a neat idea they do have a lot more circuitry and parts. Tube sockets, wiring, resistors and capacitors, Not to mention, extra current required for the tube filaments. I thought when you added it all up, a SS high voltage supply seems to be a viable alternative that could be purchased complete and with .very low noise output.
Not necessarily...
Yes, you do need space on the chassis for at least one, and in a vast majority of cases, two sockets for the VR tubes. But most solutions using VR tubes require only one additional resistor (to set up strike voltage) and one capacitor. By themselves, VR tubes to not draw ant current, and they do not have heaters, as their physical operating principle is different from "normal" tubes. And again, If you are talking about voltage regulation for B+, unless your amp's total power consumption is under 40/30ma, VR tubes are not suitable for that, and SS regulator is smaller, cheaper, more efficient. But we were talking about tube cool glow factor, and in this case, SS cannot beat VR tubes. Plus, they are useful, as I mentioned, as G2 voltage regulators for power output tubes.
Cheers, Paul
 
Well I'm taking the plunge after being encouraged watching YouTube KT88 series by Mark @ Blueglow, I have started ordering parts, the Edcor transformers are the longest lead time, have a box of parts already in. At the very beginning now, have the IEC in the chassis, watching for deliveries daily!
 
I built mine almost 8 years ago and it's still going strong. With the right preamp and speakers it sounds fantastic.

preamp for starters will be my updated Pat-5, I am a little concerned with the efficiency of my Lsa 1's, even with my small room setup. I currently drive the speakers with a rebuilt ST 120. I am getting pretty excited, the waiting for parts is killing me. I've had to buy so many things like chassis punches, thermal strippers, oscilloscope, variac etc. The list goes on and on. I will add a chassis layout drawing for my build, if I had one I could drill and punch the chassis.
 
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preamp for starters will be my updated Pat-5, I am a little concerned with the efficiency of my Lsa 1's, even with my small room setup. I currently drive the speakers with a rebuilt ST 120. I am getting pretty excited, the waiting for parts is killing me. I've had to buy so many things like chassis punches, thermal strippers, oscilloscope, variac etc. The list goes on and on. I will add a chassis layout drawing for my build, if I had one I could drill and punch the chassis.
I will be ordering parts hopefully tomorrow, I've been wanting some thermal strippers and chassis punches because it sucks drilling out but it gets the job done. I was lucky enough to get an analog discovery 2 for free yesterday though. Are you going to follow Blueglow's schematic down to the T?
 
I will be ordering parts hopefully tomorrow, I've been wanting some thermal strippers and chassis punches because it sucks drilling out but it gets the job done. I was lucky enough to get an analog discovery 2 for free yesterday though. Are you going to follow Blueglow's schematic down to the T?

I wish I could get a discovery for free, have been looking into those, my old used scope only has one working channel, i have prof friend looking for another scope for me. Yep to the T, i have memorized the dozen videos, printed out the bom and schematics. I enjoy the way Mark teaches. I am adding the theristor he mentions, a few cosmetic differences. BTW I picked up my my pace strippers for $25 off ebay and my greenlee punches for $16 & $25, not bad.
 
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I wish I could get a discovery for free, have been looking into those, my old used scope only has one working channel, i have prof friend looking for another scope for me. Yep to the T, i have memorized the dozen videos, printed out the bom and schematics. I enjoy the way Mark teaches. I am adding the theristor he mentions, a few cosmetic differences. BTW I picked up my my pace strippers for $25 off ebay and my greenlee punches for $25 & $30, not bad.
Those are good deals! Yeah, the analog d2 wont replace my scopes but it will be used as an audio analyzer and a transistor curve trace sometimes. I got really lucky because a friend that used the analog d2 for a course last year told me he never used it after and I let him know I'll put it to good use so he just gave it to me, of course my wife and I will be taking him and his wife out for some dinner and bowling to say thank you. The kt-88 amp will be used for a party this spring, I will be building some 100db speakers to get the most out of it, I'm thinking along with a subwoofer it should get the party going. I always use a cl-80 on all of my builds, I will also be bypassing all caps with a pio and will have a switch to have two different bias points so between that and switching rectifier tubes I should be able to bias el34,6l6,kt66,kt77,kt88, and to some extent kt120. Hope your build goes well, this could be my favorite for years to come.
 
Understand, I was going to build one of the new st70 kits but this one caught my eye, my lsa 1's may not be the best choice but my hobby room is 10X10 so i'm hoping, . got a ton of parts in today but partsconnexion and Edcor will be a while. BTW for the IEC I just taped a template to the chassis and used a dremmel with a cut off wheel, no breakage and it worked great. When I get the chassis mechanically done will post some pics.
 
Understand, I was going to build one of the new st70 kits but this one caught my eye, my lsa 1's may not be the best choice but my hobby room is 10X10 so i'm hoping, . got a ton of parts in today but partsconnexion and Edcor will be a while. BTW for the IEC I just taped a template to the chassis and used a dremmel with a cut off wheel, no breakage and it worked great. When I get the chassis mechanically done will post some pics.
I've have been thinking about this amp most of the day, I very well may end up making mono blocks to get the most out of these. I really want to be able to run kt 120 and 150 with some reasonable current and figure the best way will be going to mono blocks. I noticed Mark used a 5AR4 rectifier to help achieve the 460 volt plate voltage but he is also running the outputs each somewhere around 80 mA so somewhere between 160-180 mA when you also factor in the driver tube and that seems to be pushing the 5AR4 a little too hard for my taste so monoblocks would give me a little more voltage to play with, would be easy on the rectifier ever while running kt 150. Yeah for IEC I just use a nipper tool but it does suck on a steel chassis.
 
Guys ... I've just swapped the 5V4 on my SE KT88 for a 83 mercury vapour!

To my ears, it remedy those HF metallic vocals and above all, bass went deeper!

I'm extremely exhilarate with the result ..... it's Shangri-la!

Power supply: 375-0-375vac~83~10uf~10H~50uf~50uf.

Wondering if the first cap of 10uf is correct or not !? B+ is now 416vdc.

Cheers!

Zekk
Hi Zekk,
Could you provide more info on how to use a 83 in your amp? A schematic would be nice. Also, do you notice any added noise. The 83 is known for being "noisy ."
Regards,
David
 
Has anyone tried using a pair of 816 MV rectifiers in the PSU?

Yeah, I know it will require adding an extra switch to apply the high voltage once the 816 filaments have warmed up but I'm seriously considering this option.

I've been reading a lot of posts on Thomas Mayer's "VinylSavor" blog (he really likes MV rectifiers) and think this would be a nice addition.

Thoughts?
 
Has anyone tried using a pair of 816 MV rectifiers in the PSU?

Yeah, I know it will require adding an extra switch to apply the high voltage once the 816 filaments have warmed up but I'm seriously considering this option.

I've been reading a lot of posts on Thomas Mayer's "VinylSavor" blog (he really likes MV rectifiers) and think this would be a nice addition.

Thoughts?

Oh, here's the schematic. Nothing changing really, just the 816s.
 

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Just wanted to show my new version of the amp...

This is a "baby" KT88, mostly because I did not have Edcor CXEs on hand, so I used GXSE, on which I replaced the bells. As you can see, there are two separate chassis: one for PSU, and one for the amp. The amp is SS rectified, in a CLC-LC-CL configuration: One big choke (200mA) after rectifiers and two chokes (90mA) for each channel. Separate reservoir caps for output stage. Caps for the input stage are on the amp chassis. The PSU also has a voltage doubler running off 5VAC winding for 12V, which I need for VU /circuits/meters.

The amp itself is assembled on a separate chassis. Unlike my other builds, this one has plenty of space to work on, and allowed for much neater layout. I also added a headphone/speaker switch and some circuitry to match low/mid/high impedance headphones. I also added the VU meters (not pictured) and install them in the case. This is my first build of an amp separating the PSU from the amp itself, and I really like the way it came out. I will be building the cabinets for them today/tomorrow...

Interesting thing is that there is zero hum. I listened to the amp around 3:00am this morning, and could not hear even a slightest hint of it from my Cornwalls. This surprised me, as I have not applied any of the standard anti-hum measures: artificial tap for the heaters, did not raise heaters above ground, etc. I wonder if this is because of the PSU/amp chassis separation.

Anyway, just wanted to share, since I have not posted any of my builds lately... :)

Cheers, Paul
 

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Interesting 'modularity' with your build.
Wish there was a decent custom chassis maker available to us. Chassis makers want us to use what they offer rather than offering us what we want.
 
Interesting 'modularity' with your build.
Wish there was a decent custom chassis maker available to us. Chassis makers want us to use what they offer rather than offering us what we want.

There are good chassis makers, but the the business of custom chassis (or anything custom) is not cheap or inexpensive. One of my lifelong friends owned a small metal shop. He made several custom chassis for me, and we discussed this topic. The process of actual chassis making is not that laborious or time consuming. He had a waterjet cutter and bender and a welding station. The most time consuming aspect of making individual order chassis was the design/setup time. First, you have to lay it out in a CAD program, then import it into CAM program, setup tooling, etc, and only then cut it. All in all the timing broke down into 2 hours of prep time and 15 mins of cutting. Then another 20 mins of bending and 30 min of soldering/cleanup, etc. So considering his shop time was $100/hour, a decent quality chassis would cost around $300, not counting painting, electroplating or anodizing... Obviously, a different chassis would require the similar time efforts. The only way it could work for a reasonable price (around $100-$150) is when the customer does all the prep work himself, including generating G code on the same CAM sw that he uses in his shop (Mach3, in his case). Second issue is he needs a steady stream of custom orders, and it is just not there. Most of his work was small - medium size (50-500 parts) orders where he'd make most of his money. On such orders he'd set up once, and run the machines all day...
My friend of 30 years passed away in April from a heart attack... Collapsed right on the shop floor... I miss him dearly...
 
Just wanted to show my new version of the amp...

This is a "baby" KT88, mostly because I did not have Edcor CXEs on hand, so I used GXSE, on which I replaced the bells. As you can see, there are two separate chassis: one for PSU, and one for the amp. The amp is SS rectified, in a CLC-LC-CL configuration: One big choke (200mA) after rectifiers and two chokes (90mA) for each channel. Separate reservoir caps for output stage. Caps for the input stage are on the amp chassis. The PSU also has a voltage doubler running off 5VAC winding for 12V, which I need for VU /circuits/meters.

The amp itself is assembled on a separate chassis. Unlike my other builds, this one has plenty of space to work on, and allowed for much neater layout. I also added a headphone/speaker switch and some circuitry to match low/mid/high impedance headphones. I also added the VU meters (not pictured) and install them in the case. This is my first build of an amp separating the PSU from the amp itself, and I really like the way it came out. I will be building the cabinets for them today/tomorrow...

Interesting thing is that there is zero hum. I listened to the amp around 3:00am this morning, and could not hear even a slightest hint of it from my Cornwalls. This surprised me, as I have not applied any of the standard anti-hum measures: artificial tap for the heaters, did not raise heaters above ground, etc. I wonder if this is because of the PSU/amp chassis separation.

Anyway, just wanted to share, since I have not posted any of my builds lately... :)

Cheers, Paul

That's gorgeous, Paul. Nice job.

What type of connectors are you using for the PSU to the amp? I'm still debating on whether or not to create a separate chassis for the PSU for my amp and am curious what you're using?

-bob
 
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.
 

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