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70W 6L6GC low distortion amp by scott reynolds of tavish designs

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I’ve never personally been a fan of the toroidal output transformers. Like SS devices, they go from a linear state to a grossly non-linear one rather instantly when they reach the limits of their capabilities— at low frequencies anyway. The article specifically highlights that point with its design. I know they have their advantages, and their shortcomings can be allowed for, but for me I think the advantages are outweighed by their disadvantages. YMMV.

Dave
 
This would be a good study to learn how the design does parallel push pull and the thinking behind it. That behemoth of a power supply, holy cow, old school--but then again it shows some serious knowledge of how things are to be done. I bet it measures and performs very well within its limits. Terribly complicated, appears it uses two feedback loops. The driver stage exhibit some complexity in and of itself with the inner feedback loop. Lots of places to make mistakes.

I would never build this amp as is if I was looking for something to build. Rather, I'd opt for a much simpler design even if it means less power. Of course, I also prefer to drive a Toyota Camry rather than a Dodge Challenger Hellcat. ;)
 
Other than the output transformer used, the driver stage, output stage, and power supply reminds me very much of the topology that ARC used in the 80s. It’s hardly identical of course, as ARC made use of more modern devices all around, output stage local feedback, and cross coupled stages before the driver stage — but it does have design elements that together certainly appear to be influenced by ARC designs that preceded it by nearly two decades.

Dave
 
i do not know engineering and circuit design at all, but i have had some exposure to scotts designs, and they run from clever tweaking and optimising a classic phono circuit (vintage, classic) to sophisticated phono amp design like the adagio (i own both the adagio and vintage). i hear that the minotaur is quite unusual as well.

i wish i know this stuff better. i read thru the article,m and, in my ignorance or maybe despite it, the design seems well-thought-out and a little off the beaten path. im so very curious.
 
rustnrot said:
I've never been a fan of parallel push-pull output tubes. Rather than 4 6L6GC's per channel, you could build a simpler amp using 2 KT88's per channel and still get 70 watts.

This appears to be the replacement for the PAT-4004
https://mennovanderveen.nl/index.php/nl/producten/push-pull/vdv-3070-pp-detail

Here is a so-called 8B "replica" using the same OPTs.

https://pearl-hifi.com/06_Lit_Archi...een_Menno/Marantz_8b_Replica_w_Plitron_OT.pdf
Click to expand...

A pair of KT88's is only(at best, assuming they can make ratings) 42W, 2x 6L6GC is 60W, and this will allow more idle current. My solution: 4E27's for 75W of plate dissipation...and an easy 55W Class A amp... :) Not easy to carry tho.

Douglas
 
Probably one of the most well-known 6L6 quartet - foolproof, simple and efficient driver and power stage, able to fine Hi-Fi performance with suitable transformers and tweaking :

upload_2023-5-14_13-28-28.png

A+!
 
PakProtector said:
A pair of KT88's is only(at best, assuming they can make ratings) 42W, 2x 6L6GC is 60W, and this will allow more idle current. My solution: 4E27's for 75W of plate dissipation...and an easy 55W Class A amp... :) Not easy to carry tho.

Douglas
Click to expand...

i just looked up that tube. far out, man!
 
ceylon said:
does it appear the tavish should outperforms the hifi-modded fender twin reverb or vice versa?
Click to expand...

Oh, I was just speaking about a much simpler design than the one proposed in Glass Audio - using a quartet of 6L6GC to produce 75WRMS as well - nothing else ! And yes, suitably modified, the driver plus power stage of a Fender Twin Reverb can be an excellent basis for a Hi-Fi amplifier project. As a guitar amplifier, the power output already reaches 85WRMS for 5% distortion, which is not so bad...

But it's me, OK ? :D;)

T
 
I'm with Dave G. Toroidal outputs and an overly complicated design that looks straight out of the ARC playbook - no thanks. I'll add that PPP 6L6GCs in each channel is an even less practical topology now than when this amplifier was designed over two decades ago. A pair of EL34 can produce the same power level.

Jack
 
On some level I can appreciate the engineering talent to produce such an amp, but on the other hand I really just don't need or want to deal with anything that complicated.
 
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