300b

[Guy Pettigrew]

It would be great if Andy Grove could have another look at the WAD 300B pse design.

Perhaps, with his genius transformer designing skills, he could make the mains and O/P transformers even better than they are!!

Guy

[Ianm2]

why?

he already supposedly designed the wad tx's, of which many got rather hot and buzzed, along with the godawful preii tx's, and some of the output tx's aren't the most stable, whilst that is ok, it should be noted that they are built to a price, without saying that and saying he's a genius tx designed casts a shadow on that.

not criticising him, just making it known to say that if you claim they are from a fantastic hand and perform poorly, reason needs to be made clear, otherwise disappointment, disillusionment and doubt arise

what do yours do that aren't adequate?

the cores on those 2 are huge, I doubt you could get much better in that respect, so that really only leaves the HF performance of the output tx.

why not commission him yourself? he's supposed to do designs, or try sowter

[Guy Pettigrew]

Hi Ianm2

Not saying the 300B transformers aren't great.

But I've just upgraded my Phono 2 and Pre3 with Mr Grove's new transformers, and been very impressed.

Stands to reason if he worked on the 300B transformers and circuit we could expect the amp to be even better than it is now!

Guy

[prince of darkness]

Not sure where your coming from here Guy. Andy Grove did design the 300B pse circuit and transformers and as Ian suggests both were probably a lot less compromised than some of the other WAD products.
I suspect that to improve significantly on the original transformers would be rather expensive.

[Guy Pettigrew]

Hmmm

Firstly, Andy Grove has significantly improved the transformers for the phono 3 and pre 3, when compared with his original designs for the transformers in the phono 2 and pre 2.

Secondly, he has designed the pre 3, which performs far better than his original pre 2.

Who's to say he couldn't make equally significant improvements if he designed a 300B PSE version 2?

Am I missing something here? Seems quite a reasonable proposition to me.

Guy

[Ianm2]

Guy, there's not a huge amount he can do with the circuitry.

its an optimised design, pentode was chosen for hi gain, w.electric originally used that driver in the 91 circuit, but it gives a hi output impedance, hence the 2nd stage andy used was a cathode follower to lower that, it may actually sound better without the k follower, perhaps darker, but you may have to 'disconnect' the grid bias bit and just cathode bias, and perhaps lose a little power.

pse is generallly accepted to be not as good as plain s.e., its better to go the latter and choose speakers, rather than go for power. try pulling out one 300b and see what you think, it won't hurt at all, harmonic distortion will rise a bit, and power fall, but you may prefer the effect of one tube.

its limited by choice in pentodes, he rehased it for nick lucas with ef86, and 5687, he's always good with his choices for circuitry, that I suspect would improve it in the way you are seeking.

the problem is availability of valves, and the chassis is 'cut' for small 6au6, so you would have to rebore with a hole cutter.

there are a few ways to drive a 300b, but most would be a total redesign, and a totally different amp, not ness. better, my take would be something similar to his audionote 845 pse, can't recall the name, ankoru? or drive the 300b with a 2a3, or even el34, and a first stage, 5687 to drive that, I think that's probably similar to the 845 circuit, perhaps one of them transformer or choke coupled, but price would go up considerably.

its mains supply is also a little low, which would need a new mains tx.

thorsten wrote a great guide on 300b/set drive methods, its all pretty much in there the options, and would pay to study it

the pre's transformers HAD to be improved, as they really were bad, the pse's are quite good, it may be poss to get better.

the preii was done in the days when wads cost cutting was at its peak, the phonostage didn't even have proper decoupling, again whether that's the designers choice, as he didn't think it was needed, but then again, a designer builds for all cases as best he can, or a production decision, all it needed was 1 resistor and cap.

300b pse isn't quite as hair shirt. still has a few weaknesss, compare to the glasshouse 300b for an optimised version.

pre3 wasn't really a rehash as such, its a totally different circuit topology, which bears no relation to the original, I would sling pse out and simply redo as plain s.e.t., I havn'et heard the glasshouse, but I dislike cathode followers, so would look to something different myself. my fave driver I have heard is 2 x 6sn7s, or 5693/6188/6sj7 pentode... loads of gain and life, if a little thick. much more you can do but its hard work finding a good driver for 300b.

it ends up where you really start to customise it, and start adding chokes for anodes, grids and input transformers, along with 2 stages of total gain, once you get past a 'basic' circuit

[Richard]

Hi Guy,
Have a look at Sowter SE12s. They look to be purpose made to do what you are asking (at a cost) but Brian Sowter will advise if you send the circuit.
Rich

[JerryT]

Originally Posted by Guy Pettigrew

Hmmm

Firstly, Andy Grove has significantly improved the transformers for the phono 3 and pre 3, when compared with his original designs for the transformers in the phono 2 and pre 2.

Secondly, he has designed the pre 3, which performs far better than his original pre 2.

Who's to say he couldn't make equally significant improvements if he designed a 300B PSE version 2?

Am I missing something here? Seems quite a reasonable proposition to me.

Guy

Hello Guy

My sympathies are with you!

AG probably would do much better version of 300PSEor 300pp, as he has when revisiting other WAD/WD designs. However any designer has to respond to production costs. Mid life WAD products suffered because the production components were not always up to the spec. of the prototype. This seems particularly true of transformers etc. which are very expensive.

Having looked at the Glasshouse stuff though, my question is whether I can afford it!.

Jerry