...and then there were 300Bs

[Erik Mandaville]

Jim:

Modifcations and experiments are not always an improvement. I know you've heard me say this many times, but what is an improvement for one person might not be for another. There was discussion not too long ago about changes done to the original Dyna ST-7, in the belief that it was lacking in certain respects -- which for some may have been a completely honest and genuine impression. However, I know of people who really like the original circuit as was designed, but perhaps cleaned up a bit with parts new parts, yet parts matching the values of the original.

Same goes for the MKIII. I have a variety of schematics from past audio DIY articles, where changes in tube choice for the front end were made, as well as several other things, all in the name of improvement, yet there are people who truly like the way the amp was first designed and made.

Your question about your 300B amp: There is absolutely a chance that the sound of the amp might change with different parts (I'm reluctant to call them better, because they may not be, even though they might cost more). My point is that 'different' does not automatically mean better. It's often sort of a gamble. I've purchased very expensive parts in the past that did change the overall character of the component, perhaps even just slightly, but I did not care for the result, despite the fact that I spent more on the 'upgrade' than I did the first time around.

Same goes for this 300B amp I built into the Moondog chassis. I did the majority of work at a time where I didn't want to afford costly capacitors and resistors -- and didn't. My thinking is that a design and concept is much more important than the types/brands of parts used to realize the component, however will often change types once a design is done to alter here and there. In this case, the very inexpensive Orange Drop capacitors I'm using, which happen to be .15uf/600v capacitors, are working perfectly well for me. I could buy much more expensive brands, but might change the sound in a way I don't like. The change I still want to try has to do with input/driver design, not the kind of capacitor I use.

So, in the end, this is an example why learning a little DIYing, and learning how to solder can be helpful. It puts you in the position of changing capacitors, resistors, coils, transformers -- whatever the part happens to be -- as often as you want until you find what you like. If you try one thing and it doesn't work out, it's certainly not a failure per se'. It teaches you that what you thought might be a good idea needs improvement!

What did you have in mind for your amps?

Erik

[mike stehr]

Mike:

I know you're already familiar with this, but that DC supply should be straightforward.

Voltage source -- full-wave bridge -- ripple filter -- Load.

*Adjust ® as needed for 7.5 volts and suitable power rating. 10,000uf on either side of the dropping resistor should do well. There are a few other ways of doing this, too.

You could use a reasonably priced filament transformer of say 8.5 volts/few amps.

Erik

Dropping resistor comes off the (+) out from the rectifier and into the pi filter. 10Kuf @16 volts are on either side of the choke.

Thanks EriK,

I was thinking of using the 801A's in a amplifier, but I don't have the output transformers with the right primary impedance.....maybe a DHT pre-amp down the road.........

Nonetheless, I do have the OPT's with correct primary impedance/wattage for a single-ended SV811-10, and PS transformers with a good 800 volts to swing them. The thoriated tungsten filaments will need DC heating @ 6.3 volts at around 3 amps I think.

I'm pondering way ahead here......I'm in the middle of a Eico ST-70 project.......

[jt1stcav]

What do I have in mind for my amp?

That's just it, Erik...I don't know, for I've never heard another 300B amp to use as a reference point. There's probably nothing wrong with the amp I have as is...it certainly sounds good to my ears, but then again the source, preamp, and my Triangles could all play a part in the overall soundscape of my system, not to mention the tiny room it's in, and modifying any of their parts may or may not help.

Lacking DIYer skills certainly doesn't help matters any, but I always read about modifications being made to a component to improve it's sonic signature...where does one draw the line? Like you also mentioned, there's that chance the sound will change after mods are made...and not for the better (to my ears).

Unlike you (and both our fathers), I lack those essential electronic skills, therefor I would never chance the butchering of parts I would inflict on my amp, which is why I would never attempt such a feat in the first place. Even the most basic of electronics escapes me, so for me to experiment on my amp with different parts to capture a sound that's a marked improvement would never happen. Frankly I thought it was more cut and dry than that...use better, more expensive caps and iron, and better sound always prevails!

Guess the ol' saying is true...if it's not broke, don't fix it! Yet y'all do your mods on your gear and hear improvements...guess I just wanted to jump on the bandwagon too. That's okay, I can't afford to anyway.