Drake L4 good for what power?

[ka2zni]

Hello everyone. I am anxiously awaiting the arrival of a Drake L4 with the original 3-400z's in the 'ole girl. I will replace with new RFP 3-500's when these wear out, but in the mean time wanted something with a smaller footprint in the shack for times when I didn't want to go into the next room to fool with/tune the floor model henry amplifier I got and refurbed not too long ago.

100% modulated even with the smaller power supply I should be able to run a cool 200 watt carrier all day long I would think, or this being a bit optimistic? Either that or run 150 watt carrier and bump the modulation up to 150%? The xmtr I use will hit the baseline pretty aggressively at 200% but coasts pretty good at 150% ... I like to stay closer to 100% though when I can.

Not familiar with the Amplifier or the older Amperex 3-400 z's, so any opinions, comments or just plain experience with using this amplifier would be of help.

This thing is in great shape and I cannot wait to have a smaller footprint amplifier to play with from time to time and it's always nice to have something new to play with anyways!! 

[KD6VXI]

The L4s I've played with made fine little 1200 to 1400 watt PEP amplifiers, for AM based use.

I use from 5 to 1 to 6 to 1 PEP to carrier ratio, though.

I know 11 meter operators that cruise them at 400 watts carrier, with 1600 watts PEP being the norm.  They are overdriving them, and they are using the 3-500s in them, but the power supplies will take it.

I believe from reading on other reflectors, however, that the power supplies in them are slightly better than the SB220s, though....  About 1200 watts, instead of the 600 watts in the SB220.

Another thing you NEED to do to ensure the maximum efficiency in that amp is redo the bias network.  50 to 60 mils per tube is all you need for Class B, and the efficiency shoots WAY up.  You also have an excess of drive, so you need not worry about drive levels.

KD6VXI

[ka2zni]

The L4s I've played with made fine little 1200 to 1400 watt PEP amplifiers, for AM based use.

I use from 5 to 1 to 6 to 1 PEP to carrier ratio, though.



KD6VXI

very good and thank you for that information... Than a 200 watt carrier with 150% modulation will take me too 1200 watts than. That's right where I wanted to be with this little beauty.

Thank you for the Tube bias info as well... When we get the new 3-500's in we'll watch that. And, in the mean time we'll have fun with the Amperex 3-400's as well until we do replace 'em.

I guess from what I have heard the Amperex 3-400 was supposed to be a pretty good tube.

thanks again!

[The Slab Bacon]

A good healthy L-4B will easily cruise along at 300W carrier @100% mod with no problems.
Peter Dahl makes a replacement plate transfoma that will do 3500+v on high tap. Add that transfoma, a good pair of 3-500s and a little bias work and they will SURPRISE you plesantly!! At the higher plate voltage they run much more efficiently and are actually happier. Just be sure you have good airflow around the tubes.

                                                                                     The Slab Bacon

[ka2zni]

Thanks for that info, will keep that in mind for down the road... going from 150 watt carrier to 300 watt carrier should be about a 3db gain in signal strength.. I'll start with a 150 watt carrier x 6 and than go from there and see what happens.

I also thought about adding extra cooling, was wondering if it is better to pressurize the cabinet or put a muffin fan atop and exhaust the air?? Didn't think it would be wise to get too much cold air blowing directly on the tube and thought I may get a more favorable result exhausting it...

Just a thought.

[KD6VXI]

Putting a muffin fan above the plate circuit is beneficial, especially above 40 meters.

The tank coil can get pretty warm on 10.  Especially with any mismatch.

KD6VXI

[ka2zni]

Very good ... I have a high volume muffin fan... and was just trying to figure out the best placement. I was under the assumption that used as an extraction fan would be best... But everything I have read says just the opposite, So will have to figure where to place it although I read that any exhaust heat needs to be kept OFF of the Tank coil- So that just confirms what you said KD6VXI   


So I will probably mount it on the right side, and it can blow across everything, hit the tubes last and out the other side although with chimneys being installed I don't know how much good it will do if any on removing any heat from the tubes themselves... So we'll just have to play with it.

Thanks for all the good info, keep it coming if there's any more out there! 


Here's the Drake L4 I won
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=300144863760&ssPageName=STRK:MEWN:IT&ih=020

[KD6VXI]

Something else to keep in mind, that I believe I read on here.

Blowing air across something adds dust a LOT more than sucking air across it. 

If you place two fans together, or a fan loading the intake of a blower, you will get more airflow, as long as the fan can supply enough to the blower.  Taking two fans and putting them together increases airflow, as does putting one on the intake, and one on the exhaust.

KD6VXI

[ka2zni]

Yeah that was the trade off problem I read... I can try loading the blower with the other one, this is a big healthy fan... Try mounting downstream of the tubes if that don't work, and than the forced air method from the other side of the case. What would be nice is if the squirrel cage was enough to do the work in the 1st place. we'll have to try it out and go from there.

Definitely don't want to burn this one up, next year though am going to implement a pair of 3cx1200a7's in the shack for what I really want to do.

[KD6VXI]

A good friend of mine in San Diego came up with a dual 1200A7 mod for the L4 series of amplifiers.

He expounded on, and fixed, the Pittenger articles.  They make a nice desktop 5kw, but EVERYTHING in the RF deck needs replacement.  Of course, a power supply as well.  The sockets are reusable, though

I ran a 3X8877 amp in the 80s, got tired of tube replacement, and on Reid Brandon's advice, I moved to the 1200A7s.  I had more than enough drive (using a Valiant II) for either tube.  The 8877s where replaced almost yearly..  The 1200s never where replaced.

Ended up trading it for a 4CX10,000 amp in pieces.  Don't know what happened to it now, probably relegated to "10 meter" use back east...

If you are purchasing tubes new, get a YC tube or something similiar.  Get a tube that you can use the grid as a dummy load when necessary   (the 1200 makes a fine dummy load for small rice box exciters, 4CX5000s run as triodes for bigger driver radios).  Just my two cents worth.

I miss the look of glass in the shack, though.  Something about 4X4-1000s just LOOKED impressive.  MUCH more impressive than the coffee can in the box now.


KD6VXI

[W3SLK]

Kevin said:

Hello everyone. I am anxiously awaiting the arrival of a Drake L4 with the original 3-400z's in the 'ole girl. I will replace with new RFP 3-500's when these wear out, but in the mean time wanted something with a smaller footprint in the shack for times when I didn't want to go into the next room to fool with/tune the floor model henry amplifier I got and refurbed not too long ago.

You may have put the cart before the horse here. I'm not 100% sure but I'll bet that the chimneys for those 3-400Z's are designed for the low profile type tube. When the 3-500Z's first came out, they were in the same glass envelope as the 3-400Z. Later production made a slight increase in the envelope size of the 3-500Z's. I'll venture that you will have to get the larger chimneys to accomodate the bigger 3-500Z's.

[ka2zni]

Kevin said:

Hello everyone. I am anxiously awaiting the arrival of a Drake L4 with the original 3-400z's in the 'ole girl. I will replace with new RFP 3-500's when these wear out, but in the mean time wanted something with a smaller footprint in the shack for times when I didn't want to go into the next room to fool with/tune the floor model henry amplifier I got and refurbed not too long ago.

You may have put the cart before the horse here. I'm not 100% sure but I'll bet that the chimneys for those 3-400Z's are designed for the low profile type tube. When the 3-500Z's first came out, they were in the same glass envelope as the 3-400Z. Later production made a slight increase in the envelope size of the 3-500Z's. I'll venture that you will have to get the larger chimneys to accomodate the bigger 3-500Z's.

I questioned this on purchase, it appears that the RF Parts made 3-500z's are the same size as the old 3-400 Amperex tube, the owner purchased a pair of 3-500's for another amp and tried them, exact fit...

If I go with an Amperex or taylor though I am out of luck.

Thanks for the info.