My Winter Project

[bricktop]

I wonder if those open baffle speakers might actually prefer the relatively high output impedance :scratch2:

I just hooked them up to the OB speakers, I didn't want to do it until i was sure the amp was safe. Before they were hooked up those pioneer HT speakers.

The amp does agree pretty well with these. Big waste of power potential tho, the amp does get pretty warm. Bass is better than the heathkits, very tight.

 

[bricktop]

I admire your lead dress. Everything looks well planned out and organized.

It might look like that, but I kinda just improvised as I went along. The only thing I did plan was AC on one side of the OTs, DC/signal on the other, and CCS right next to the 6CL6s. It got pretty cramped at the end, the chassis is only 2 inches deep.

On a related note, I scored 11 pairs of tektronix matched 6CL6s on ebay a short while ago. That should last me a lifetime with this amp.

 

[bricktop]

ARRRR, she glows!

(Insert pirate smilee here)

 

[Urizen]

BT, I've been following this build since the beginning.

Very impressive!:thmbsp:

 

[jaymanaa]

ARRRR, she glows!

(Insert pirate smilee here)

No need to chop wood for the fireplace.

 

[bricktop]

No need to chop wood for the fireplace.

I've kinda been using as a handwarmer:thmbsp:


Output stage schematic attached

 

[bricktop]

Square waves!

might try tweaking feedback to get rid of the overshoot on the 1KHz wave, i donno

Distortion measurements:
1 Watt 1KHz = 0.18% THD+N
20 Watt 1KHz = 2.5% THD+N
source is 0.1% THD (HP204C)
using HP333A

 

[bricktop]

OK, did a little bit of feedback experimentations over the past few days. Added plate feedback and lightened up on the gFB. New square waves attached. Measured THD+N @ 10 watts, 1KHz, now it is 0.28%. I think the 20 watt measurements are a little close to the crossover point and is not a good indicator of amp clarity, which is mostly noticed with lower powers.

anyway....

 

[bricktop]

Ok, scrapped the plate feedback. It had good results, but it created hum and power supply noise because the plates of the EL34s see 6vpp of power supply ripple during idle. Did increase global feedback, distortion figures are the same (0.27% THD 1khz, 10watts). Here is the updated schematic. I think I'm done tinkering with it. It sounds great, just gotta mount the frame and bottom panel now.

 

[jaymanaa]

Nice job man!:thmbsp: I would have commented on the scope pics, but I don't have a clue what they mean. I did finally get a usable scope (10mhz Tektronic) with a probe and manual, but I don't have a clue what to do with it. Luckily I live close to Echowars and I think he's gonna give me some pointers (like how to turn it on and such). Are you planning to attend the fest this spring? I'd really like to hear that dude.

 

[bricktop]

Nice job man!:thmbsp: I would have commented on the scope pics, but I don't have a clue what they mean. I did finally get a usable scope (10mhz Tektronic) with a probe and manual, but I don't have a clue what to do with it. Luckily I live close to Echowars and I think he's gonna give me some pointers (like how to turn it on and such).

Scope skills will definitely come in handy with amp restoration/repair/troubleshooting. With square waves, the basic goal is flatness and no overshoot or ringing.

Are you planning to attend the fest this spring? I'd really like to hear that dude.

I donno, I guess that's something to think about. Maybe, , it's about a 7 hour drive, might be a fun road trip.

 

[bricktop]

I finally got some ambition to finish this. Just quickly did the bottom panel and mounted the wood trim. There is about a 1/2 inch gap between the wood trim and surface, hopefully improving cooling by letting some air flow up from underneath it. Feet are #4 rubber stoppers from Lowe's, which were better than any other actual feet they had

This should be it, done and done:thmbsp:

 

[currituckco]

Wow, that looks great!

 

[coman61]

Man, Thats some nice work there Bricktop. How about a few more Pics.:thmbsp:

 

[bricktop]

How about a few more Pics.:thmbsp:

I'll take some more when I get home from work today

 

[SPL db]

Very, very nice! :yes: :thmbsp:

Scott

 

[saltwater]

Brick I didnt know, this is ............. amazing! Didnt think you were working on somthing! :thmbsp:

 

[bricktop]

Man, Thats some nice work there Bricktop. How about a few more Pics.:thmbsp:

As promised

 

[coman61]

Very nice. Old school speaker jacks. What are they tapped for, 4 and 8 ohm?Does that red rocker illuminate when powered up?

 

[bricktop]

Very nice. Old school speaker jacks. What are they tapped for, 4 and 8 ohm?Does that red rocker illuminate when powered up?

They're 8 and 16 ohm jacks. Yup that's a rat-shack illuminated rocker.