Best cap to cathode tube bypass is …..

[Katapum]

Hi all,


I’d to know what is the best cap to cathode tube bypass. The 300B amp needs a 120uF/6.3Vcap.
I have in my place:

Panasonic FC
Rubycon YXF
Sanyo oscon
Elna RJH

Any comments or suggestions are very welcome (and sorry my English).

Katapum

 

[DigitalJunkie]

I dunno about the best,but I've heard the Oscon's are pretty good for cathode bypass duty.I havn't tried it myself though,yet.

6.3V ? are you sure about that? Seems low to me..

 

[SY]

Where in the circuit is this used?

 

[andyjevans]

You can get 100uF in motor run caps. Big, but good. I use ICW polypropylenes rated 160uF. Big but very good.

 

[Katapum]

Where in the circuit is this used?

in input stage (not in 300B stage).

You can get 100uF in motor run caps. Big, but good. I use ICW polypropylenes rated 160uF. Big but very good.

Amp has no room to big caps.


Katapum

 

[summilux]

Andy,

I've been thinking about using motor run caps for bypass. Were they noticeably better sonically than good elctrolytics (BG or other)?

Jonathan

 

[SY]

Why not lose the cathode bypass cap and bias up the input tube in some cleaner way?

 

[Katapum]

Hi,

Why not lose the cathode bypass cap and bias up the input tube in some cleaner way?

😕

Could you elaborate?
(Input tube is a triode; the amp has only two stages with no feedback.)

Katapum

 

[SY]

If you can sketch out the input stage, perhaps we can look at some alternatives.

Sorry, I just hate cathode bypass caps. Nasty things.

 

[Giaime]

If you can live whitout 3dB of gain, what's the problem? Just leave it out! Stuart, am I wrong? Does the first stage need to be fully redesigned? Just make up for the lost gain with a little increase in plate resistor (or tube change)...

 

[SY]

It depends on what's happening with the next stage. Cathode degeneration reduces gain and also increases output impedance. You can't just pull the cap out without knowing what else it's going to affect.

 

[Katapum]

Amp input stage

 

[SY]

Tubes? Component values? Coupling? Load?

 

[Katapum]

I’d to know what is the best cap to cathode tube bypass. The 300B amp needs a 120uF/6.3Vcap. Nothing more!

Katapum

 

[andyjevans]

I've been thinking about using motor run caps for bypass. Were they noticeably better sonically than good elctrolytics (BG or other)?>>

I never tried BGs anywhere, but they were a lot better than usual electrolytics. I don't use cathode bypass in input stages - I just use a 100uF under the output tubes. Very clean and clear, and this counts when using high resolution tubes like 2a3 etc.

 

[Katapum]

Hi,

Could I reduce cap value to 47uF?

Katapum

 

[rdf]

With a CCS on the plate do you need a cathode bypass cap?

 

[SY]

With a CCS on the plate do you need a cathode bypass cap?

Try it with an unbypassed resistor. You'll be surprised at how poorly it works.

 

[Geek]

Hello,

I’d to know what is the best cap to cathode tube bypass. The 300B amp needs a 120uF/6.3Vcap. Nothing more!

Katapum

Try TV horizontal sweep electrolytics. Non-inductive and easily obtained.

You're bypassing, not coupling, should be OK 🙂

 

[rdf]

Did & was. Just so far with a triode-connected E180F though, which eventually measured best CSS+gridleak bias and left me wondering if the issue stemmed from topology or implementation.