Johnson Ranger modulator tubes

[wc4r]

I picked up an original Johnson Ranger and plan to upgrade the modulator tubes to the 'recommended' 6550 tubes. Some tell me the KT88 tube (European version) is fine also.
My questions to you folks: 1-Is the KT88 an equivalent replacement in this case? 2- Is there a 'best brand' such as TungSol, Sovtek, Electro-Harmonix or other commonly available (or a brand to stay away from)?
73 Joe

[N2DTS]

There are also KT90 tubes.
I forget the brand, but I got a bunch from Czechoslovakia which were supposed to be better quality then the USSR or China ones.
I think they used to be $15.00 each, much higher now...

[N2DTS]

The ones I got are Ei/magnoval  from Yugoslavia, KT90 tubes.
Those are not as wide as KT88's, but slightly taller (1/4 inch).
I use those in a 32V3 and they have held up fine.

I also have some JJ brand KT88's that have also been fine.

You can get a lot of power out of the KT90 tubes...

Both run AB1 allowing you to ditch the driver transformer...

[wa3dsp]

I used 7027A's in my Ranger mod which is the tube used in the Ranger II. Works fine and plenty of modulation. I have about a dozen Gold Lion KT88's but opted not to use them because of the size and that they were overkill based on the stock modulation transformer. I did remove the driver transformer as part of the mods and used a tube phase inverter. Two 6550's can produce well over 100 watts of audio. The Ranger is about 60 watts input on AM, maybe 70 if you push it. That is 30-40 watts of modulation audio. One could use the headroom argument but three times the required audio is a bit much especially using the stock mod transformer. On the other hand an argument for using the 6550 or KT88 at reduced power is longer tube life. They also are probably more available.

The KT88's I have would also have required some mechanical mods to the chassis due to their size.

http://www.crompton.com/hamradio/JohnsonRanger/RangerRestoration.html

[N2DTS]

But the KT90's are not wide like the KT88's are, so if space is limited, they might do.
Often it comes down to what you can get at a sane price these days.

[w4bfs]

don't overlook Sovtek 5881 .... cheap and they like higher B+ than 6l6