SR45 amplifier

hi Paul... not Taran, but using MQ HN grid chokes in the SR-45 too... using a RelCap TFT for coupling... the grid choke were a noticable improvement...
 
Im using a vcap cutf coupling cap. I think the grid choke was the biggest improvement i made with parts. Going from a russian teflon to vcap was 2nd.
I put in cobalt grid chokes. I should compare to the nickel. I put ni grid chokes in sex amp and PDG amp but not as noticeable a difference.
 
Awesome Paul,

Very much looking forward to it.

The Mexican Bottlehead community has been discussing this on our own discussion "forum" (a crazy emails chain) and thought that the BeePre experience could lead this project to become an SR300B (2 watter though).

Saludos
 
There are some incurable tweakers here, aren't there?

What I meant was, what capacitance - not what type of capacitor. Remember, I do have an engineering background ... I still like numbers when I can get them!

re: the 2-watt 300B ... many things are under study ...
 
I too think that the nickel BCP-16 was the largest improvement.

Using mine behind a .22 Russian K40
 
braubeat said:
As long as we're pushing the envelope how about a Quickie (ie. battery) BeePre.

Michael
Click to expand...
Quickie IS a battery BeePre! Well, it's a DHT single gain stage with no output transformer, straight from the plate - the simplest possible tube gain stage. You could try a Type 31, which is a real triode instead of a triode-wired pentode and needs 2 volts for the filament - a single-cell lead/acid would be appropriate, and I think they exist in D-cell format. It would probably be happier with more plate voltage, but should work at Quickie conditions. Said to be EXTREMELY microphonic but I haven't tried it or heard one.
 
In my amps the stages are RC coupled and the grid chokes go from grids to ground -- I thought this was thepreferred way to use a grid choke as opposed to LC coupling?  Any advantage either way?  I would assume with the grid-to-ground config the value of the coupling cap would not have to change.

Speaking of the split personality of this thread, might it be useful to have a separate thread either for the legacy or new design -- I can see new folks getting pretty confused by this thread at some point in the future.

-- Jim


 
Jim, I am not clear on what you said. Normally the grid choke would replace the grid leak resistor (usually 249K or 270K in Bottlehead power amps), from grid to ground. (Actually I mean from the grid stopper to ground; nothing but the stopper actually connects to the grid pin.) I suppose that, by analogy with how we describe power supply filters these days, you might properly call these C-R or C-L coupling rather than the traditional RC/LC terms.

There are two main technical effects of a grid choke:

1) Since it has inductance, it will resonate with the coupling capacitor. That resonance is damped mostly by the effective parallel resistance of the choke, which comes mostly from eddy-current losses. There is an argument for leaving the grid leak resistor in parallel with the grid choke so that a known minimum amount of damping is provided. This resonance means the bass response rolls off more steeply while remaining flat through the audio frequencies, so faster recovery from transient overloads is likely to occur.

2) At midband frequencies the impedance of the grid choke is higher than the resistor it replaced. This places a lighter load on the driver, possibly reducing its distortion. Leaving the resistor in parallel will eliminate that effect.

I have not done any measurement or listening to evaluate this tradeoff - which is why I wanted to know the capacitance that seems to work. If there are experiments with leaving the resistor in parallel, I would be most interested in the results as well!

With the longer chassis, and the DC heater supply, there may be a suitable location for the grid choke, near the driver and far from the power transformer.
 
Paul,

Ok, third time on this later when the oxy codone wears off and I'm a bit more focused.

I'm just going to avoid posting for a while until I can truly grok this :-).  I think we're saying the same thing but I thinkk I used the wrong terms in the wrong places.

-- Jim
 
Ok, we are saying the same thing, except you have a grid stopper in there and I'm not sure I remember seeing one in there -- unless it is the same as the series RC coupling combination.  But the amp is downstairs and has juice on it, so I'm not going to go poke around right now.  And yes, now I can see why it would effect the RC resonance point.

Thanks for getting me on the right track.

-- Jim
 
Me again, any updates Paul?  The Bottlehead team has been busy with so many releases lately but my eyes are on this baby!
 
Nothing much. I'm struggling with the wiring plan, since I moved parts away from convenient locations to locations where they will remain cooler and last longer. The amp is part of a larger plan, and there are some issues with making sure that derivative designs are going to be workable.

I think I may have a few too many balls in the air and will have to drop a few ...  :^)
 
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