New PP amp...

[randy warren]

Well..... I'm in the middle of taking an old time tube radio repair class which has been fun and has given me the courage to work on an old Fisher 500B that I inherited from a family friend. I've fixed a couple of old radios along the way which has been fun. To bad there isn't more interesting stuff on the AM band.

I'm also fiddling with a PP 845 amp. With 700 - 750 volts on the plates looks like I can get 30 -40 watts without trying to hard. Driver stage isn't as hard as it would be with a higher power amp and 700 volts doesn't scare me quite as much as 1200. Got a lot of experimenting to do though. I was hoping that with a PP amp you could use AC on the filaments and it would cancel out if you wire it in phase but it doesn't work as well as I hoped, sigh...... I'll have to talk with Dave B. about that RF filament supply.

Charlie

where are you taking this class, in Bowie?

[Stuart Polansky]

Well, Roscoe, I'm building something but not what you mean.

I KNOW what you mean!

So many tube projects waiting in the wings until this is running and off to the paint shop!

Attachments

[Stuart Polansky]

BTW, Tubedriver, I don't have the GOLD valve train, mine is blue! Transparent valve covers really are available! Hilarious!

Attachments

[Stuart Polansky]

Transparent valve covers

http://www.rolandracing.com/id25.html

[Guy]

Wow, Thanks, Everybody for offering loaner phono amps! You want to be careful (ask Charlie) - I borrowed his phono amp, stopped working on mine and kept his two years! Not that Charlie ever was upset or angry with me: he's too even tempered.

Roscoe - thanks for verifying the battery situation. I was going to check the amp-hour rating of batteries today but you've already answered my question. I remember a tube-radio kit long ago that used (among others) a small group of AA batteries for something (heater, bias?) I also figured I'd add an AC-to-DC power supply as an alternative to battery, or possibly a charger, to compare amp noise.

Charlie, where can I learn about this radio-repair class? It might be worth driving to your area to take such a thing (of course, snow will start soon.)

Tube Driver and TomP: thank you for graciously offering your loan of phono amplifiers! Please see disclaimer at start of message, and let me consider your offers with that in mind - I feel like a freeloader, and I might be forcing you into the role of Enabler!

Let me look at Roscoe's link, too, and see what I'm in for.

Ask for transparent valve covers, that's something I never considered. I figure they'll be all oily anyway, but I could check the oil quality that way. My rockers are gold because I'm too cheap to upgrade to the Stuart's blue Scorpion rockers, but that's the way I would have gone. Now it's getting too cold to paint in the garage - fire up the heaters, I guess.

[Roscoe Primrose]

Is this the first time you've tried the "Pearl" Triode" circuit?
Have you heard it used on other amps before?

Yes, this is the first time I've either tried or (to the best of my knowledge) heard the Pearl Triode Trick.

Roscoe

[tomp]

No problem with the return date on my phono pre. It is just taking up space on a shelf right now.

Tom

[charliewphelps@gmail.com]

The class is at the National Capital Radio and TV Museum located in Bowie. They have one class on Monday evenings and one on Saturdays. I heard about it from my office manager's husband (who teaches it). Small world.

So far I've fixed an "all american five" for my brother and a AM/FM tube radio that I've had lying around for years. I started working on the Fisher and have replaced all the problematic caps and changed the bias supply as per suggestions of "The Fisher Doc". Hopefully I'll be able to fire it up tonight at class - with a nice variac with ammeter.

Charlie

[Stuart Polansky]

The class is at the National Capital Radio and TV Museum located in Bowie. They have one class on Monday evenings and one on Saturdays. I heard about it from my office manager's husband (who teaches it). Small world.

So far I've fixed an "all american five" for my brother and a AM/FM tube radio that I've had lying around for years. I started working on the Fisher and have replaced all the problematic caps and changed the bias supply as per suggestions of "The Fisher Doc". Hopefully I'll be able to fire it up tonight at class - with a nice variac with ammeter.

Charlie

Class sounds very neat. I'd like to do that as well. Can you post any enrollment info?

A little suggestion: after the usual variac startup, and before a full line voltage startup, consider starting with an incandescent lamp in series, with similar power ratings as the Fisher. one last step to avoid "booms", magic smoke dispersal, exploding fuses and caps.

Slick

[Roscoe Primrose]

Now it's getting too cold to paint in the garage - fire up the heaters, I guess.

I've got a pair of 833s that'd make a great garage amp/heater

Roscoe