Kegger/blueglow kt88 project

[JohnT123]

So is that the end of discussion on these amps? I'm still trying to evaluate mine and also wondering about any changes that people have made to the design. Mine didn't follow the Blueglow plan, it was a composite of ideas I got from 2 of Mark's builds and my own ideas about the driver section.
All I can say about it, is that it sounds great, runs cool and is technically solid. Maybe. No idea about distortion or frequency response. I can't even find a company in the area that could test it. I have a bad habit with guitar amps where I'm in continuous development. I can't stop tweaking the design. I'm afraid that it will carry over into this realm. I've already started collecting parts for the next 2 versions.

 

[Ruidoso Bill]

So is that the end of discussion on these amps? I'm still trying to evaluate mine and also wondering about any changes that people have made to the design. Mine didn't follow the Blueglow plan, it was a composite of ideas I got from 2 of Mark's builds and my own ideas about the driver section.
All I can say about it, is that it sounds great, runs cool and is technically solid. Maybe. No idea about distortion or frequency response. I can't even find a company in the area that could test it. I have a bad habit with guitar amps where I'm in continuous development. I can't stop tweaking the design. I'm afraid that it will carry over into this realm. I've already started collecting parts for the next 2 versions.

I sure hope the discussion isn't over, I may build another. I actually need to finish this one up, still going to replace the power transformer and get it up on a scope, I got so excited when it started working I just had to hook it up! I have been looking at youtube videos about looking at it with a scope and figuring out it's output, look for distortion etc. I really want to build a tube preamp, Mark had mentioned it was in the plans for this year, not as many preamp designs as power amps.

John what are you using for your inputs

Mine now has 40 or so hours on it, played all last weekend and I do a lot of work at home so have had it running, trying different music and really enjoy how great it sounds. Mine does not run too cool, gets pretty warm and wondering about heating up the preamp above. I would love to hear about your driver section design. If I build another see no point in the volume control, I like adding a partition near the center for isolation and adding some rigidity to the chassis, these transformers are no lightweights!

 

[JohnT123]

I guess we're the official Blueglow fan club. I put mine on a scope but the traces were not pretty. A good sine wave until about 5 watts of output, but I don't know if the signal generator and scope are working 100%. In fact, I plugged the signal generator directly into the scope and still got some weird looking waveforms. I trust my test equipment enough to find problems but it's not good enough to measure the effect of subtle design changes.

Instead of a single dual triode feeding both outputs I've used a pentode, in triode mode, for each output tube. I got the design from a Svetlana white paper on building a phono pre and the component values from a Mazda application sheet for the EF86. I love the sound of the EF86 and I've been using them in guitar amps for years. This arrangement yields amazing channel separation with zero hiss or hum.

My stereo 70 didn't have a volume control and I like having one. It seems to be more versatile and allows me to run the amp direct from my CD player. Like you, I'm wanting to get a tube pre. Hoping Mark can get to it this year but I'm collecting parts as I go and may start one on my own. I have a Hafler DH101 pre and a Technics pre. The Technics is actually quite good but could use an overhaul at 40 years of age. The Hafler is restored but it's still a SS device.

 

[Ruidoso Bill]

I guess we're the official Blueglow fan club. I put mine on a scope but the traces were not pretty. A good sine wave until about 5 watts of output, but I don't know if the signal generator and scope are working 100%. In fact, I plugged the signal generator directly into the scope and still got some weird looking waveforms. I trust my test equipment enough to find problems but it's not good enough to measure the effect of subtle design changes.

Instead of a single dual triode feeding both outputs I've used a pentode, in triode mode, for each output tube. I got the design from a Svetlana white paper on building a phono pre and the component values from a Mazda application sheet for the EF86. I love the sound of the EF86 and I've been using them in guitar amps for years. This arrangement yields amazing channel separation with zero hiss or hum.

My stereo 70 didn't have a volume control and I like having one. It seems to be more versatile and allows me to run the amp direct from my CD player. Like you, I'm wanting to get a tube pre. Hoping Mark can get to it this year but I'm collecting parts as I go and may start one on my own. I have a Hafler DH101 pre and a Technics pre. The Technics is actually quite good but could use an overhaul at 40 years of age. The Hafler is restored but it's still a SS device.

Wow, an ST-70, that's where all this tube interest started me thinking. I ended up doing a total rebuild of a Pat-5 and ST-120, got everything I needed from Dan at Akitika, great guy to deal with, he offers a Pre kit with great specs, the PR-101 but it's SS, still a very impressive preamp. Maybe I should restore something old.

Technics in the day built some pretty nice equipment, my SL-23 is 43 years old on the outside but all newly rebuilt inside, works flawlessly, I bought it new, gave it to a kiddo, he gave it back and I rebuilt it.

I lucked out on test equipment, my old Tektronix 922 had only one channel working, new brother in law is a professor and told me the had tons of test equipment waiting for disposal, he grabbed me a Tek 5110 that looks new, and a Wavetek 186 generator, I like my older Global Specialties 2001 generator. Also have an old Hickok I-177B and Eico 667 tube tester, nothing pro level here but good enough for what I do.

 

[Ruidoso Bill]

I was thinking about building one more KT88 Set with some changes. I contacted Hammond Mfg about getting a chassis 17 X 10 X 3 in primer, no powder coat, not easy and they want 10 minimum, does anyone know of another mfg that I can get a steel chassis in primer?

 

[Heffa]

So is that the end of discussion on these amps? I'm still trying to evaluate mine and also wondering about any changes that people have made to the design. Mine didn't follow the Blueglow plan, it was a composite of ideas I got from 2 of Mark's builds and my own ideas about the driver section.
All I can say about it, is that it sounds great, runs cool and is technically solid. Maybe. No idea about distortion or frequency response. I can't even find a company in the area that could test it. I have a bad habit with guitar amps where I'm in continuous development. I can't stop tweaking the design. I'm afraid that it will carry over into this realm. I've already started collecting parts for the next 2 versions.

It's definitely not over for me.
I haven't even had time to actually test my amp with speakers yet, my free time is so limited due to life and kids and other IRL stuff.

I just quickly hooked it up to a signal generator and a dummy load last weekend, and the output was totally garbage
Just before I had to leave I realized I had a (almost, 2-3 ohms) short of the left signal input to ground, and found out that I had melted the heatshrink on the ground of my tiny coax cable right at the ALPs pot. Didn't have time to fix it more than just physically bend the signal lug out of the way a little, hope this was the reason for my garbage output.

Anyway, my plan is to also add two analog VU meters to the front of my amp, and I will add bleeder resistors to the large caps too. I have already built two buffer PCBs for the VU meters, and a small voltage doubler/rectifier board for the +12V power to these two boards.

The next step is probably to build a tube pre-amp, either I'll wait for Mark to start his build or I might do it myself.

 

[Autobahn]

Finally have collected everything to build my KT88 Amp. I used Mark's parts list he put on his Blueglow Electronics webpage. Plan to mirror his build. The only part I have different is the EDCOR Transformer Part# XPWR144 (240v Primary 380-320-0-320-380 secondary @ 200mA, 6.3v @ 3.5A, 5v @ 3A) since I live in Germany now. I've checked my Mains Voltage, and it is always around 224 VAC. I wonder if this will affect my build any, or if I may have to change some things?
I have a lot going on right now so probaly wont begin my build for a couple more weeks.

Michael

 

[Ruidoso Bill]

Heffa & Mical, & John,
kinda cool we are at close to the same point, I need to disconnect it from my system and put it up on dummy load and take a good look at it on the scope, haven't done that yet but it sounds so good a little afraid it will look like garbage on the scope and prove I have no ears left, if that's the case I will continue to build, just won't notice if is's bad.

Gotta do something about a tube pre.

 

[Ruidoso Bill]

It's definitely not over for me.
I haven't even had time to actually test my amp with speakers yet, my free time is so limited due to life and kids and other IRL stuff.

I just quickly hooked it up to a signal generator and a dummy load last weekend, and the output was totally garbage
Just before I had to leave I realized I had a (almost, 2-3 ohms) short of the left signal input to ground, and found out that I had melted the heatshrink on the ground of my tiny coax cable right at the ALPs pot. Didn't have time to fix it more than just physically bend the signal lug out of the way a little, hope this was the reason for my garbage output.

Anyway, my plan is to also add two analog VU meters to the front of my amp, and I will add bleeder resistors to the large caps too. I have already built two buffer PCBs for the VU meters, and a small voltage doubler/rectifier board for the +12V power to these two boards.

The next step is probably to build a tube pre-amp, either I'll wait for Mark to start his build or I might do it myself.

I will be very interested in your VU meter progress, please keep us in the loop.

 

[Ruidoso Bill]

It's definitely not over for me.
I haven't even had time to actually test my amp with speakers yet, my free time is so limited due to life and kids and other IRL stuff.

I just quickly hooked it up to a signal generator and a dummy load last weekend, and the output was totally garbage
Just before I had to leave I realized I had a (almost, 2-3 ohms) short of the left signal input to ground, and found out that I had melted the heatshrink on the ground of my tiny coax cable right at the ALPs pot. Didn't have time to fix it more than just physically bend the signal lug out of the way a little, hope this was the reason for my garbage output.

Anyway, my plan is to also add two analog VU meters to the front of my amp, and I will add bleeder resistors to the large caps too. I have already built two buffer PCBs for the VU meters, and a small voltage doubler/rectifier board for the +12V power to these two boards.

The next step is probably to build a tube pre-amp, either I'll wait for Mark to start his build or I might do it myself.

I can attest to the fact these things are pretty tough, all my problems and the worst was a degraded rectifier tube, I'll bet it's fine.

 

[Heffa]

I will be very interested in your VU meter progress, please keep us in the loop.

Sure, I'll try to take some pictures or even a video of them this weekend - they are already tested and working outside of the amp.
The reason I didn't add them to the chassis right away is I am a little worried that they might affect the sound of the amp. I want to try them with real load and measure the amp before I cut two more holes in the front of my chassis.

 

[Heffa]

Finally have collected everything to build my KT88 Amp. I used Mark's parts list he put on his Blueglow Electronics webpage. Plan to mirror his build. The only part I have different is the EDCOR Transformer Part# XPWR144 (240v Primary 380-320-0-320-380 secondary @ 200mA, 6.3v @ 3.5A, 5v @ 3A) since I live in Germany now. I've checked my Mains Voltage, and it is always around 224 VAC. I wonder if this will affect my build any, or if I may have to change some things?
I have a lot going on right now so probaly wont begin my build for a couple more weeks.

Michael

Where did you get your Edcor transformers here in Europe?
I couldn't find any seller of them so I went with Hammond transformers for my build.

 

[Ruidoso Bill]

Where did you get your Edcor transformers here in Europe?
I couldn't find any seller of them so I went with Hammond transformers for my build.

Guess I'm lucky, Edcor is a 3 hour drive for me, in fact my wife was born in Carlsbad, NM

Only thing it saves me is shipping, still just one in their queue.

 

[Autobahn]

Where did you get your Edcor transformers here in Europe?
I couldn't find any seller of them so I went with Hammond transformers for my build.

I ordered them straight from Edcor. I retired from the U.S. Military, but still work with the military here in Germany. So I'm allowed to use the military postal system. They built and shipped them to me in about 5 weeks. No Custom or Import Fees since it is thru the U.S. system.

Michael

 

[Ruidoso Bill]

I ordered them straight from Edcor. I retired from the U.S. Military, but still work with the military here in Germany. So I'm allowed to use the military postal system. They built and shipped them to me in about 5 weeks. No Custom or Import Fees since it is thru the U.S. system.

Michael

I used to go to Germany when I worked for Raytheon, guess I went there 20 or so times. Always enjoyed it.

 

[Blueglow]

Just stumbled onto this thread. Subscribing so I can help answer any questions going forward.
Glad to see people building this.
Mark

 

[Autobahn]

Just stumbled onto this thread. Subscribing so I can help answer any questions going forward.
Glad to see people building this.
Mark

Glad to see you here Mark. I really like your Youtube channel. I 'll probaly have some questions when I get into building it, but I'll try to keep any minimal. I can see your very a busy man, and you also need to take it a bit easy with your Recovery. I hope you have a none to stressful recovery.
Michael

 

[Ruidoso Bill]

Just stumbled onto this thread. Subscribing so I can help answer any questions going forward.
Glad to see people building this.
Mark

Glad you found it Mark, must feel good to have so many following your build!, some better and then there is me. Hope you're on the mend. Love this amp!

 

[JohnT123]

I consider this one my prototype. The next one will be slightly different and have the meters. I've been waiting for 9 weeks for the meters and driver boards. 8 weeks for the next Edcor shipment so I have time to plan.

 

[Heffa]

These are my VU meters that I'll try to use. Please ignore my ugly buffer boards, I managed to etch them mirrored so had to put all components in reverse and the OpAmp on the backside
At least they works, so that's fine for now.
The meters themselves fit in a 34mm round hole, they are pretty tiny. Also, they are back-lit,so I think they look nice.