GK71 amp

[ratbagp]

At the far end of the spectrum in build quality from the recent GM70 amp but on the same planet in terms of output tube, I have just completed a GK71 SE amp. It uses some techniques that I have not used before that are designed to lower the weight of the amp.

You can read about it here.

http://audioratbag.blogspot.com/2016/01/the-heart-attack-special-6s17k-v.html

I hope you find it interesting.

ray

[rock4016]

Excellent write up Ray! I'm glad you are doing better.

[Guy]

I agree: your article is a good read - it's like I'm working along side you.

[ratbagp]

The amp is gradually breaking in and continues to improve. It is less dynamic than the 6C33C amp and perhaps a bit more natural. If I am around I will bring it to the next meet.

It is definitely much easier to lift than the 6C33C amp. Carrying very heavy objects for more than a few seconds is still uncomfortable.

The stacked smps power supply continues to fascinate me. I suspect it would make a good test setup for trying out new ideas without having to build the power supply first. Just create a stack of twenty or so and just use the range(s) you need. It would be simple enough to create more ac heaters for the standard voltages. The halogen bulb transformers are cheap.

ray

[rock4016]

How does your 6C33 amp sound compared to your 829B amp?

[ratbagp]

I prefer the 6C33C amp which is more dynamic and has more power and detail. I suspect the Tannoy transformer is much superior to the RS line transformer in the 829B amp.

I am pondering what I should do about the OT for this GK71 amp. I would like something light weight with specs of 5k - 7k, 16 and 8 ohm taps, able to handle 120 ma or so. Since I bi-amp, low frequencies are not a priority. Ideas would be welcome.

ray

[rock4016]

Transcendar has a 5K that weighs 6.5lbs and 4-8-16 secondaries. Its the TT-021-OT,

It can handle 140 mA.

I use the lower power version in my EL34 se amp, that you heard at Fritz's place.

[Roscoe Primrose]

There seems to be an inconsistency in the driver section of the schematic... 60V on the plate with 3ma and a 51K plate load resistor would net 213v rather than 144v. Looks like 1.6mA with those voltages...

Roscoe

[ratbagp]

Good catch.

I just went back to Eric Barbour's article in November 2001 Audio Express and I see that I have written on the schematic 1.5 ma that I calculated years ago. I will adjust my GK71 schematic.

I am still not sure whether I really like the amp, despite the incredible detail. Still, it is interesting to listen to even if it is not as relaxing as the 6C33C amp.

For transformers I have substituted a pair of old huge Audio Note 2.5k transformers that I run off the 4 ohm tap for 8 ohm speakers or the 8 ohm tap for 15 ohm speakers. The transformers are each heavier than the amp itself so I have each transformer outboard in separate boxes.

ray