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[56oval]

Originally Posted by mhouston

I was given a box of very old tubes. In the mix was a new pair of black metal tube RCA 6N7s (tested 80%). There seems very little schematics for this tube as a preamp but lucky my electronics engineer mate knocked up a design.

The preamp runs from a 18V 2.2A wall wart and uses a step down tranni backwards to produce 255VDC HT. The sound is punchy, deep driving bass, clear, clean and crisp. Best preamp I have ever made. Dead quiet at idle. I have called the preamp "Heavy Metal" after the metal tubes.

I like the case .

Cheers

[mhouston]

Originally Posted by 56oval

I like the case .

Cheers

You want to ear it? Let me know when.

[56oval]

Originally Posted by mhouston

You want to ear it? Let me know when.

Cheers mate I'll let you know .

Mal

[richwalters]

Photo- the 0.5mm thick brass plate escutcheon of my Vampire 500W..a well designed amp deserves a good reflection...Being half s german, I like metallic views...makes all the difference with no screws visible on the front..compared with ally panel behind with flush set screws.
Lettering is last generation rub-on letraset alphas' and the next step is an engraver to do the job proper. It isn't as expensive as one makes out to be and I can recommend it. Amp dimens 18"x18" or ~46x46 cms.

Despite Wavebournes thread....the dilemma of where to mount vs. length/breadth etc, I prefer an uncluttered front panel....Judge for oneselves . Brass plate can be picked up in good hardware stores.-make sure it hasn't got scratches in it, though sleeks can be rubbed out with wire wool and brass polisher.

richy

[Cassiel]

Originally Posted by rcavictim

Is that part of a gun assembly from an in-line color CRT?

I have no idea where I got it from. Sometimes I like taking parts from dead machinery for no apparent reason. I just find some parts interesting. Maybe some day I will do some 'art' with electronic parts, although I doubt it. In the meantime trash keeps cluttering my basement.


Good job, richwalters.

[mhouston]

@richwalters: Nice work. Did I miss something but what is the tube configuration and tube names??

[richwalters]

Originally Posted by mhouston

@richwalters: Nice work. Did I miss something but what is the tube configuration and tube names??

This amp isn't to be "messed" with..and requires premium grade components.
Raw meat overview:

8x EH KT90; 4x 12BY7A;2x E80CF; 1xECC83
double parallel push-pull.
Williamson config amp with active CCS diff driver (12BY7A)
E80CF as concertina/triode config 1st stage.
Selectable pfc power supply 1.5kW rated, operates at 75Khz;
Amp can be use in bridge mode for MI enabling 500W+ mono.
Raw data;
4 selectable B+ operating conditions:-
B+ 210V low power low quies 15mA per o/p tube;
B+ 300V ...50+50W 100mA quies per o/p tube close class A Hifi,
B+ 410 MI standy condit- near tube cut off.
B+ 600V mono bridged full 525W continuous sinewave, just over 250W per channel AB1, 75mA quies per o/p tube, full output close to 0.2A per tube.

The driver stage operates at a perm 360V at 60mA both channels. This is current dumping.
Logic circuit enables Hot switching i.e Neg Bias volts switches with whatever B+ setting.

Measured 1dB below full power, resp-1dB@ 17Hz-50Khz (-3dB 100Khz)...... with input transformer -3dB 50Khz
18dB/oct HP input filter (butterworth) -3dB 15Hz (good for octave shifter deep keyboard work)
Distortion, nom 0.2% 1Khz per channel at full AB1 output; class A condition at 45+45W ~0.05%.
Unconditionally stable; nom global feedback 19.5dB can accept another 14 dB before instability sets in...Stable for electrostatics.
Square wave asymettry near optimal, 3rd harmonic Fourier criteria easily acheived. Loop damping and circuit Q optimised.
Damping factor 20, ~4 ohms
hum & noise ~-75dB below full o/p per channel.
Crosstalk 15Khz ref 150W per ch = -80dB, (other input s/c) requirement for studio console work. This is a tough one to acheive.
Power supply HF harmonics barely undetectable on spectrum -100dB down. 100Hz ripple ~-80dB down.
Input sensitivity +6dBu (for full o/p) balanced 10K imp XLR per channel
Other features; Yes it has 2W carbon resistors as grid stoppers.
Watchdog for bias fault and B+ asymmetry, input mute# 20 sec warm up, AC brown out, reset per missing cycle, (quite common on land lines).
Layout designated for long life; electrolytics and ventilation in properly assessed locations;
Mechanical, weight ~55kg#120Lbs; 4mm ally plate and bracing used around transformers.
Build time ~6months in evenings.

There is a considerable amount of test data and doc which I'm currently softwaring.

Output transformers; standard M6 laminate, customed spec'd with paper isolation and grade 2 wire, 18 sectioned designs; designed frequency response 15Hz-50Khz; 4 sep output winding configurations. Majestic Transformers, Poole, Dorset UK. In amplifers such as this one, the hand wound transformers were quite well matched by the same person on the winder resulting in identical R/C phase correction components on each channel.
In the past, as the yellow polyester tape replaced kellogs paper, over time the leakage capacitive actually started to rise as the self algamating properties were taking place. This is the reason that Quality output transformers for tube amps should only be quickly end dipped to seal against moisture and NOTvarnish vacuum impregnated as per mains types.

The unexpected ? Amplifiers of this class come in for some disection.The extra wide frequency response was the big surprise.The 12BY7A diff driver has a superb performance in dealing with output stage Miller, but with the unexpected high freqency bandwidth, this did show some interaction between various makes of input tubes
ECF80,7643,6BL8 but best results were with E80CF. This tube wasn't designed for audio, and quite alot are microphonic. In practice, the proximity of the unscreened input tube should have been place slightly further away from the capacitive voltage swing of the output tube anodes.
In circuits with such a wild bandwidth as this one, the grid stoppers do a vital job in curtailing a wild response (designed on a stage to stage basis) and will effect the square wave shape, as did the output stage A-g2 zobels. These values wern't arbitarily chosen, as je higher the frequency, the zobels and grid stopper values do effect the slewing.

The B+ of 600V is an annoying voltage...requiring stacked up electrolytics and 600V rated semis are ruled out favouring 1kV types. Fortunately there are quite alot of 1kv devices in the TO220 package around...space is a premium.
The associated dangers of building power amps which use high Joules is an issue for some and any recklessness with shortcircuits which result in component destruction require eye & hearing protection.

Like the previous 5, I enjoyed every minute of puting this one together.

This is the last of.... Hurrah Williamson !

richy

[lenamit]

This is a Christmas gift I am DIY to my wife.
6AQ5 pp 12AU7 ,EF86

[richwalters]

10+10 Watts correct ? What's the under view........that's where the quality is...

richy

[Bigun]

Originally Posted by Tomy

The colum is PS of amplifier . It has 3 separate voltage with the kens for 3 stage of amplification and it has no electrolytic capacitors

My GOSH !

This thing is extreme - huge cabinets full of high voltage capacitors - looks like a doomsday device