I've been a lurker for some time but here is my first post. Hi everybody.
I thought I would give a quick walkaround of my new overkill tube amp. Just what I wanted for my little shop. Comnoz
https://youtu.be/jWbWz3y0ZSU
I thought I would give a quick walkaround of my new overkill tube amp. Just what I wanted for my little shop. Comnoz
https://youtu.be/jWbWz3y0ZSU
Hi Commoz,
that is really something, congratulation. Could you post any further data? A schematic would be great.
Regards KlausB
that is really something, congratulation. Could you post any further data? A schematic would be great.
Regards KlausB
Going by the style and components used, I'm guessing you've spent a bit of time around broadcast transmitters? Power output?
At this time the only schematic is in my head.
My schooling was around 1970 -communications electronics -when tubes were the only way.
A general rundown:
The power supply: [the hard part]
The power supply has series Fet regulated voltages at + and - 150, -500, +385, +500, and +600. The fet's reference voltage comes from VR tubes.
Each channel has it's own iron choke and capacitor bank for decoupling at each voltage level.
Bias voltages are from a separate transformer and adjusted at the power supply. The adjusting potentiometers provide reference for fet regulators and failure mode would be at -150 volts.
The B+ is from two 1KVA transformers -paralleled after the SS rectifiers and charging a bank of 12 -1800mfd 450 volt capacitors to 2000 volts. They are located under the amp chassis.
It also supplies 4 times 5 volts at 14.5 amps for the big tube filaments and multiple 6.3 volt supplies for the smaller tubes. All filaments are AC and hum is non-existent.
The tube filaments have 1/3rd voltage when the power is off to keep things warm. Several time delay relays with soft starts for the transformers provide staged startup and voltage and currant monitors will shut it down if things are not right.
The amp:
Preamp is two 2021 tubes, one per channel, with the elements of each tube in parallel.
Invertor is four 2021's, two per channel with the elements in parallel and 4n900 fet followers. CCS's in the cathode.
Drive is by four triode strapped 6BG6's with 4n900 Fet followers.
500 volt plate supply and 150 to -500 volt fet supply.
Output tubes are 4-250's in the video with 2000 volts on the plate and 600 volts on the screen. With these tubes it makes 150 watts per channel with a 40Hz sine wave at 3.5% distortion. Distortion goes up to 5% at 185 watts.
I also have 4-125's or 4-400's that I have used.
I am driving speakers with a 2 to 3 ohm impedance through Hammond .5KVA IC transformers -two per channel. [I was surprised at the results I got using these in-expensive transformers]
It is the most pleasant sounding amp I have owned and drives the Carver AL3's easily with additional dual VC 12" woofers in the old Infinity cabs and
a pair of planar loaded horns in the rafters.
Build time has been around 2 years of late night work. Comnoz
My schooling was around 1970 -communications electronics -when tubes were the only way.
A general rundown:
The power supply: [the hard part]
The power supply has series Fet regulated voltages at + and - 150, -500, +385, +500, and +600. The fet's reference voltage comes from VR tubes.
Each channel has it's own iron choke and capacitor bank for decoupling at each voltage level.
Bias voltages are from a separate transformer and adjusted at the power supply. The adjusting potentiometers provide reference for fet regulators and failure mode would be at -150 volts.
The B+ is from two 1KVA transformers -paralleled after the SS rectifiers and charging a bank of 12 -1800mfd 450 volt capacitors to 2000 volts. They are located under the amp chassis.
It also supplies 4 times 5 volts at 14.5 amps for the big tube filaments and multiple 6.3 volt supplies for the smaller tubes. All filaments are AC and hum is non-existent.
The tube filaments have 1/3rd voltage when the power is off to keep things warm. Several time delay relays with soft starts for the transformers provide staged startup and voltage and currant monitors will shut it down if things are not right.
The amp:
Preamp is two 2021 tubes, one per channel, with the elements of each tube in parallel.
Invertor is four 2021's, two per channel with the elements in parallel and 4n900 fet followers. CCS's in the cathode.
Drive is by four triode strapped 6BG6's with 4n900 Fet followers.
500 volt plate supply and 150 to -500 volt fet supply.
Output tubes are 4-250's in the video with 2000 volts on the plate and 600 volts on the screen. With these tubes it makes 150 watts per channel with a 40Hz sine wave at 3.5% distortion. Distortion goes up to 5% at 185 watts.
I also have 4-125's or 4-400's that I have used.
I am driving speakers with a 2 to 3 ohm impedance through Hammond .5KVA IC transformers -two per channel. [I was surprised at the results I got using these in-expensive transformers]
It is the most pleasant sounding amp I have owned and drives the Carver AL3's easily with additional dual VC 12" woofers in the old Infinity cabs and
a pair of planar loaded horns in the rafters.
Build time has been around 2 years of late night work. Comnoz
A couple of late edits.
The preamp and inverter tubes are 6021's not 2021's
There are actually 18 -450v 1800 mfd volt capacitors instead of 12 in the B+ supply. Comnoz
The preamp and inverter tubes are 6021's not 2021's
There are actually 18 -450v 1800 mfd volt capacitors instead of 12 in the B+ supply. Comnoz
comnoz, those black/red buttons look terrific! I guess when the black's being pressed some relay's clung! shakes the floor, and the lights dim for a moment ))
The Hammond IC trafos look very alike to Allen-Bradley control circuit ones, what is IC? cant find any info. I agree that the Hammonds priced on par with Japanese boutique trafos beat the latter on sound quality, have personally done some testing on this.
The Hammond IC trafos look very alike to Allen-Bradley control circuit ones, what is IC? cant find any info. I agree that the Hammonds priced on par with Japanese boutique trafos beat the latter on sound quality, have personally done some testing on this.
comnoz, can you provide addition info, like OPT make and specs, and the idle plate dissipation of each 4-250? how is the amp in terms of hum?
The output trannies are Hammond Industrial control transformers. PH500QR.
480 volt primary and 12 volt secondary. Primaries and secondaries of two transformers in parallel appear to give approximately the reflected impedance of an 80 to 1 transformer. Less than $100.00 each.
I have tried torroid outputs wound on 1.5Kv cores but they gave stability problems due to small imbalances in the winding.
I have also tried conventional audio transformers on 2kv e-cores but they did not sound as good [to my ears] as the Hammond transformers.
I idle the 4-250s at 60 ma.
There is no hum -even with your ear next to the speaker. Comnoz
Well that and blown breakers was once a problem😱
Once I got the slow start and staging right it's happy on a 120 volt -30 amp circuit.
I run it from a 240 to 120 volt 3KVA medical isolation transformer to keep my shop wiring happy and my steel bench safe. Comnoz
Oh, the intermediate isolation Mains transformer does contribute! I have my Luxman 88U running via 650 VA toroid with 2 separate windings. Well I had to do the 120->100 V conversion anyway, but it turned out making the sound somewhat smoothier to my ear. Some others reported it kinda does some interference filtering on Mains line, cant disagree.
No, I have tried it both ways and I am not sure why it works but the tube loading works out best with both primary and secondary in parallel.
I have wound a few transformers but I am far from an authority. Electronics is just a long term hobby for me. I have talked to a couple people who claimed to know the answer but their theories did not agree. Comnoz
I have wound a few transformers but I am far from an authority. Electronics is just a long term hobby for me. I have talked to a couple people who claimed to know the answer but their theories did not agree. Comnoz
I do have a lexan cover for the tubes. Unfortunately I set it on top of one of the speaker cabs while I was doing some testing and of course it vibrated off and broke the corner.
You certainly need to think twice about any move when working around it.... 😱
Very impressive & scary! 🙂 Clearly means business. I hope at some point you will share some of the design and design process that got you there. Obviously a lot of thought and effort have gone into the design and construction of this project.
There is no question. Much of the design was skimmed from posters on this and a couple other forums that I peruse and then compiled into something I always wanted to do.
Beyond that there was an awful lot of trial and error and by guess and by golly -until it did what I wanted it to do.
So thank you to all the people who have posted their experiences for me to learn from.
Sometime I will need to compile all the little hand-drawn scraps of paper into a schematic -I might need to fix it some day. Comnoz
Beyond that there was an awful lot of trial and error and by guess and by golly -until it did what I wanted it to do.
So thank you to all the people who have posted their experiences for me to learn from.
Sometime I will need to compile all the little hand-drawn scraps of paper into a schematic -I might need to fix it some day. Comnoz
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