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Looking for an amp project

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lawbadman

lawbadman

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Joined 2003
#1
Hi guys
I got an itch to build a tube amp, just for the fun of it.

I have a Hammond 1620 (20w 6k6) output transformer so I want to use that as a starting point. I dont have the knowledge to design an amp for myself so I have been looking all over the internet for a good circuit. The circuit that I think might work is shown below.
What do you guys think of it?
Could I do better?


Thanks Lawrence
 

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#2
That looks like the Hafler adaption of the Williamson circuit. It's a good, solid design, though I'd probably increase the ratio between the two LF rolloffs defined by the RC time constants in the first two stages. You can do that by dropping C4 and C5 to 0.1uF.

The choice of 6SL7 -> 6SN7 is a particularly good one. These are VERY linear tubes.
 
#6
JojoD818 said:
In the two schematics, the first one only had a single RC for the opt tube's cathode (both cathodes tied together) while the second schematic have a separate RC for each power tube going to ground.

What's the difference? Which is better? Or are they the same?

🙂
Click to expand...

Like everything else, it's a tradeoff. If your output tubes aren't well-matched, separate resistors and caps will partially ameliorate that. If your tubes are well matched, the common RC has the advantage of any error signal being common mode (potentially slightly lower distortion).

All that said, if you buy matched output tubes, there won't be much difference.
 
#7
Question

Can I use any type of 6L6 tubes like the WGB and GC in the above circuits that I have posted?
The G tubes seem hard to get.

I have read that any 6L6 tube can be replaced by KT 66, is this true, can I use KT66 in both circuits that I have posted?


Thanks
Lawrence
 
#9
SY said:


Like everything else, it's a tradeoff. If your output tubes aren't well-matched, separate resistors and caps will partially ameliorate that. If your tubes are well matched, the common RC has the advantage of any error signal being common mode (potentially slightly lower distortion).

All that said, if you buy matched output tubes, there won't be much difference.
Click to expand...


The tubes I bought are svetlana el34 that are matched pair, however, will the pair of tubes aged together? I mean, will they stay matched during normal use?

So for a certain point of view, it would be better to just tie the cathodes and use a single RC combination.
 
#10
My own inclination would be to use a single resistor and cap (lower parts count), matched tubes, and not spend too much time worrying about what happens when they age. But, those who like to adjust their bowties using a laser-guided protractor could reasonably come to the opposite judgement.
 
#11
yummy stinkbait

The Hafler circuit has too much gain for a modern system, and you would be better off replacing the 6SL7 with an input transformer with a split secondary winding.

Separate cathode resistors and by-pass caps are better and you can add a potentiometer between R11 and R12 and a 2.5K resistor between R8, R9 and R10 and ground (ref. Hafler schematic) to adjust ac signal balance.

Lowering parts count is of little concern in the DIY realm where one builds only one amp at a time. I prefer avoiding "value engineering" where ever I can.

The bowtie comment is trolling, and I bit.

John
 
#12
SY said:
My own inclination would be to use a single resistor and cap (lower parts count), matched tubes, and not spend too much time worrying about what happens when they age. But, those who like to adjust their bowties using a laser-guided protractor could reasonably come to the opposite judgement.
Click to expand...


😀 I would really like it simple, no unnecessary complications.

thanks!
 
#13
I ended up with a pair of Hammond 1620's also, and am looking for an easy, good design to use for a first (functional) tube amp project.

I was wondering if the AN Kit4 design could be used or modified for use with the 1620 xformers. They (the 1620's) are 6.6k and (best I can tell) the AN kit4 uses something like 8k - similar to a TRAN-200 or 300?

Any advice on the subject?

Also, what experiences has anyone else had with the Hammonds,
Like, dislike?
 
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