I am wondering how well the Philco model 90 with the single 47 output performs? I have a good chance at a Philco 90 lowboy in the near future and it has the chassis with the single 47 output in it. I have to admit, the lowboy is far more compact than I pictured it and it looks like Philco crammed a lot of radio and speaker into a nice looking, but small cabinet. Actually, I might be able to do a bundle situation as this guy has the model 70 highboy I tried to get a year ago. Now he is considering selling both. Anyways, I am wondering if the 90 with the single 47 is a good performer or not.
Yes, it is. You get AVC (Automatic Volume Control), which is always a bonus, plus an RF amplifier stage (which all 90s have anyway). The single 47 model 90 is indeed an excellent performer.
Something to consider re single-ended output stages, in addition to having less than half the output of the same tubes in push-pull, is the fact that a good output transformer for them is bigger and more expensive and so they're usually skimpy. They must be gapped to prevent saturation due to the unbalanced dc current, so they need more turns for a given inductance. Unless big, they usually have higher resistance loses and bad low-frequency response. The hi-fi nuts trying to build 200 Watt, "single ended, class A" audio amps using an old transmitting triode are, as I say, nuts.
I just got my 90 highboy with the single 47 going recently. I must say, I was suprised at the performance, still needs an alignment. It is comparable to my 18 highboy in what it can pull in for stations. Not quite as rich sounding but that is probably due to the 90 having a 10" speaker and the 18 has a 12".
Looks like this unit might be a go then. There is a 90 highboy for sale in Bristol, Ohio, but it is far away and they want $200 for it. Actually, seems model 90's get priced high around here in either version (cathedral or console) and rarely are available. The one I am looking at has a presentable cabinet from what I could tell and is all there except three missing knobs and an incorrect grill cloth. Actually has all original globe or pear type Philco tubes in it except for the 80 and the 47, which I think are also both Philco tubes. I know the 80 is, forgot to look at the name on the 47 when I checked it.
I just picked up the little 90 lowboy today. That actually helps to knock two off my revised 'bucket list'. I realized I already have a model 70 in my grandfather clock radio. Pictures to come soon!
P.S. I just put up a want ad for a 15X on CL. Might have to borrow from myself to get one, but it might be worth it.
My 90L lowboy is a great DX-er. At old house I have it grounded to the radiator and a random long-wire out 40 some feet to a tree.
All the AM clear-channel stations all over US and Canada, and some not so easy to find too.
Chuck
A single ended type 47 is probably comparable to a 42/6F6 in terms of power output. I repaired a Canadian G.E J-82 some years ago and it had more then enough power output to fill the room, maybe 3 watts worth. The J-82 is roughly equivalent to a Philco 70 performance wise, maybe somewhat better since it has AVC, with a much better sounding speaker though. The 90 lowboy will probably sound better with that 10'' H series speaker then a cathedral with that stiff "Pie Pan" speaker they usually come with.
Regards
Arran
I have a 90 lowboy and it is a very good performer. Great sensitivity and selectivity.
The AVC action is excellent due to the use of the sharp cutoff 24A tubes in the RF and IF stages. Almost every station comes in at the same volume whether strong or weak, but the sharp cutoff tubes do sometimes cause cross modulation with very strong signals.
The only drawback of the 47 output when compared to a 42 or 6F6 is the low level speaker hum caused by the directly heated AC filament.