Triod istf pentodkoppling på slutsteget då? Då kommer du ner till 8w ung?
Min TT20 har detta och uppbyggnaden är ganska lik LC15, iaf samma komponenter (OT PT etc)

Andy Marshall (andrew@thdelectronics.com)

Date:
1/5/2002 10:06 PM

Subject:
Re: Yellowjackets--2203

All Yellow Jackets come with EL84 tubes. We used to use Sovtek non-military El84s, but a few years ago switched mostly to JJ/Tesla EL84s. We have had good luck with them both sonically and in terms of reliability.

What in them? Different models of Yellow Jackets have different components, but basically they have a cathode circuit (parallel power resistor and capacitor), a capacitor to block the grid bias from them amplifier, a grid reference resistor, a supplemental current limiting power resistor on the screens and, in most models, a set of Zener diodes to give a constant voltage reduction on the plate and another set of Zeners on the screens. Most Yellow Jackets, you see, have around 9 discreet components in the circuit, excluding the socket and base. Building them is more like jewelry making than like electronics.

Furthermore, there are a few different sleeves of Teflon and/or fiberglass to add insulation to the certain internal components so that they cannot short to one another.

Another consideration, in addition to the component values and ratings, is the manufacturer of the component. The Zeners that we use do, under certain circumstances, get hot enough to melt solder joints, so these components are connected using a special high-heat crimp connection that is tested repeatedly before final assembly.

You may ask how a Zener could possibly survive getting hot enough to melt solder. Good question. Most brands cannot survive this. We have found one brand of military-grade Zeners that can take this heat all day long with no ill effects. Are they expensive? Yes. Are they time-tested? Well, we have about 7000 Yellow Jackets in the field, some of them almost 10 years old, and the field failure rate is well under 1%.

Could you possibly build your own? Sure, but there are a bunch of things to keep your eyes open about. Build it sturdy, insulate the heck out of everything; don’t forget to study the temperature de-rating curves of your components.

Also, for safety’s sake, don’t even consider using metal tubing for the body of the adaptor. (We use fiberglass tubing.) If something were to go wrong, it is way too easy to get plate voltage on the body, and touching that could be very unpleasant. While I have never heard of anyone being killed by this, a few people I have heard from have gotten NASTY shocks from metal-bodied copies of the Yellow Jacket.

Be careful and have fun experimenting!

- Andy Marshall, THD Electronics, Ltd.