View Single Post
  #26   Report Post  
Posted to sci.electronics.design,rec.audio.tubes
[email protected] tubeguy@myshop.com is offline
external usenet poster
 
Posts: 15
Default Tube mono-block amp with SIX 6L6 outut tubes

On Fri, 28 Dec 2018 14:19:50 +0200, Tauno Voipio
wrote:

On 28.12.18 10:45, wrote:
On Thu, 27 Dec 2018 21:11:35 -0600,
wrote:

I'm not intending on building this, but it's interesting and makes me
wonder if someone could use EIGHT 6L6 tubes, or TEN?
(Of course adding more tubes mean bigger audio output transformers and
heftier power supplies.


Tubes may age at different rates, so the characteristics might be
quite different after a long time. It might not make sense to replace
a single (failed) tube and you may have to replace the whole set of
tubes with new tubes preferably from the same manufacturing batch.
This can be quite expensive :-)



In the 1960's, I made a guitar amplifier with six EL500's. The tubes
are not characterized for linear use, and they were not matched in
any way. Each tube had an own cathode resistor, and there was no
evidence of any overload from unbalanced operation.

The tubes had a tendency of parasitic oscillation, so I added a
ferrite bead on the control grids and an inductor-resistor parallel
combination on each plate (for constructions, see nearest ham handbook).


Back in the late 60s early 70s, I had several (self refurbished)
mono-block power amps that used four 6L6 output tubes. I did not even
know about matching those tubes. I just put in any tube marked as a 6L6.
I recall having both the glass (GC) types mixed with the black metal
ones. I always had good sound and lots of power. I do recall that
replacing the metal cased ones with 6L6GC did increase my power though.
But until I could afford new tubes, I used what I had. And even with the
new tubes, I never matched them.