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I see that the schematic for my new eiclone boards have .1uf coupling caps specified. I just happen to have several pairs of .22uf caps in my parts box. Anybody see any problem with the increase in cap size?

If they're box caps (like Wima), check the lead spacing to make sure they fit. If they are axial lead or similar (i.e., Sprague orange drop), again make sure you've got enough lead length to bend them into position without shorting against anything.

As long as they fit mechanically, they should function very well electrically. The low frequency corner (Fc = 1/2piRC) will go down by a factor of 2.2, which might be a desirable thing as long as stability is not compromised. As long as your output transformers are of reasonable quality, I wouldn't be concerned.

Thanks, The OPTs are new 4.2K x 8, 60W Edcor. I just thought I would use parts on hand if practical. One thing I did notice about the Eiclone board is that some component footprints are a bit on the small side. Still a nice product though! I know that Auricaps and Sonicaps in the .1uf are nice and small so as to fit the footprint on the board. But I seem to have so many .22 caps on hand...

100n to 220n is usually not an issue.

It's when these turkey's like to drop in 2.2uF-10uF, I'd like to reach my hands through the monitor and....

If you are building the DC-coupled version Ike, then you are OK. But if you are building the AC-coupled, LM334Z current sourced version, you will need to use .1uF caps. In a nutshell, the low frequency poles interact once the feedback loop is closed and instability can occur in the sub-10Hz region.

In a design with two AC-coupled stages *and* feedback, the first stage should get the largest RC coupling network that is feasible. The output transformer has it's own unadjustable low frequency cutoff. And the middle stage - the main driver coupling caps - should then be sized according to stability with a function generator. You need one that can sweep to 1Hz. I then sweep a sine wave from 20Hz slowly down to 1Hz while monitoring the output of the amp with an oscilloscope. If the sine wave goes unstable, or gets larger, the main coupling caps should be reduced in value. It is easy to get flat response to 3Hz with this method. Note that your calculated RC -3dB pole won't mean anything with 20dB negative feedback, and the coupling cap can end up "small", like .047uF or .022uF, with perfect low frequency response.

As far as just using what you have, I would use four of them, putting them in series to make a .11uF, voltage rated doubled cap. This seems fine to me.

Shannon