Boat anchor
 

If you can't afford a new one, just build it yourself (I told myself). Trust me, manufacturers earn every penny they ask.....
Almost 12 months to design, gather parts and build a high voltage amp.
This is my third scratch build and consists of a 76-300B-GM70
IT coupled driver for A1 to about 22 watts and A2 to about 40 watts
400v and 1200v supplies which is more than enough to kill
Coleman filament supplies
Custom chassis from Landfall Systems
Arduino control for monitoring, soft start and standby
Sounds like a gigantic 300B amp on my Khorns
http://usr.audioasylum.com/images/2/22974/img_2524.jpg
http://usr.audioasylum.com/images/2/22974/img_2523.jpg
http://usr.audioasylum.com/images/2/22974/img_2526.jpg

John.......Good to see your post. The amplifier looks excellent, very well laid out, and fine looking craftsmanship. I see it is mono, so is there a second one?

Good to see you're still building on your system, that's quite a list of equipment you have.
I sold my entire system except for the office system which consists of a couple MC60's, AR preamp, Lexicon CD, DIY Proac 5s.
My main system is Scratch built 300b monoblocks, DIY LDR preamp,modified Sono's w/synchromesh-Enlightened Audio Dac, Vinyl 1 phono, DIY turntable with graham phantom arm and dynavector XV1s. The DIY preamp switches between my 2 channel and Yamaha BDA1020 surround. The amp/preamp I built has a lot more synergy with my Khorns compared to the MX119/MC352 system I had. I spent good $$ on the best output transformers money could buy.

I decided to take on the challenge of designing and building a high voltage tube amplifier last year. To answer your question, I built two mirror image monoblocks(you can see it in the first image). The 300b amps I built 3 yrs ago were designed using tube cadd and a simple calculator. The new amps were designed using Spice simulations which saved me a lot of fine tuning. After assembling and testing I had to change the input caps to lower the voltage! I overlooked the fluctuating line voltage. An 8 volt spike in JEA line voltage put my secondary at 1280volts. I started out with 845's and 211 tubes but decided on the Russian gm-70's after shopping for NOS tubes. The Chinese versions were just not up to my standards and the gm70 was easier to drive than a 845. After 3 months of designing a circuit I spent another 3 months with parts selection and layout using autocadd. Landfall systems did a great job on cnc and made assembly much less painful. During the assembly I started some YouTube videos on microprocessor programming language. At first, it was like learning the Chinese language but started to take root after getting help from some forum members. I built a voltage divider network with opto isolation to monitor voltage and current on the gm70. This microprocessor will open the relays in milli seconds protecting my output transformer should a catastrophic failure occur. The processor also takes on the duties of soft starting the amp since the supply has about 9000joules of energy at 1200volts! I might try a couple other circuit changes that could improve on the sound. I'm not really fond of the IT coupling but it's the easiest way to handle grid current. Will try a current source and/or a plate choke-cap-grid choke.
These will be my winter amps since they put out some serious heat but will end up in a cabin in NC over the next few years as I'm looking to retire in 5 yrs.

John.......That is some serious dedication to your amplifier project. It sounds like you may still have a bit of tweaking to accomplish. Looking at your photos it is clear you dedicated a good amount of time to the layout. It is clean and efficient.

Glad to hear you are rapidly approaching retirement. Ownership of your own time is wonderful. I was so happy to walk away from the electrical contracting business. I don't miss it at all. Are you still with Munson-Bryant?

Yes, still at the same company, part owner now. Since then we grew to 120employees.
The industry has gone down hill since you retired.....and journeyman requirements were abolished.
Quality of drawings, unrealistic schedules, lack of training, poor quality, etc,etc....
I can't wait to get the hell out!

Building amps keeps me away from the boob tube and relieves stress.
My original circuit is similar to the Cary 805 except for the output/input tube and the tube rectification in mine. They used an IT but I think later designs might of changed to current source driver.

John.......Keep designing, building and refining those amps. Perhaps we will see JS Audio in prime time one of these days.

I'm impressed.

WOW...... This is awesome! I am impressed also!!!!!!! You have some serious skills........ :D

+1

Thanks guys for the thumbs up :thumbsup:
With modern computers and simulation software, its really not that difficult to design and build, triodes are the most simplistic circuits in audio. I used a free program called LTSpice, tons of support in the forums with plenty of tube models.
The magic is in the magnetics!

I'm self taught in electronics, education consisted of a 4yr apprentice program in Electrical Construction, 1st yr was theory but nothing to do with tubes or transistors. 30 years in the audio hobby did help somewhat.