Vintage amplifier wattages

[kenwashesmonday]

Rick,

Why don't you try changing some caps on the solid-state chassis first, it'll just cost a few bucks to change the electrolytics. Be careful, I think they're positive ground. Just changing the electrolytics may bring the voltage up enough that the tuner springs to life again.

The tube amps sound a bit better, but those solid state "Astro Sonic" amps sound quite good when they are operating correctly.

The 30 watt Magnavox tube amp is a good size and is well respected.
Magnavox consoles came in different levels, from 15 watts to 100 watts RMS (8 6V6 for each channel!)

Ken

 

[rickr]

Hi Ken

Thank you for your input. If the tube amp sounds better, wouldn't it make more sense to recap a tube amp and replace the solid state amp?
BTW: the tube amp replacement will be the 30 watt amp with the 4 6v6's.

Too bad I couldn't find a Concert Grand console Magnavox. I would just replace the whole console stereo with that one.
Doubt if any are out there though.
I do have a Manavox hi fi from the 1950's. Keep it down the basement in the rec room. Will count the 6v6's in that monural amp in the 50's hi-fi and post of pix of it tonight.

 

[nasadowsk]

Many people see the lackluster horsepower ratings of electric automobiles and think that they would be slow. Quite the contrary! Electric motors produce their maximum torque at ZERO RPM. Electric vehicles tend to accellerate rather quickly, and don't need transmissions. While an electric motor is putting out much of it's power out of most of it's RPM range, a gasoline or diesel engine only achieves it's maximum output within a narrow operating range.

Ahh, but at a certain point, HP does dominate And, the motors I've seen on electric cars, vs their HP ratings, makes me think that there's wishful thinking going on THERE too.

that torque amounts falls too low to pick up any more speed. If you've ever read anything about subways and electric trains, they had to install resistors in line with the electric motors so they would not pull unlimited amounts of current while starting from a dead stop. Without these, the train would jerk violently when starting off, spinning it's wheels, throwing passengers off their feet, and even possibly burning out the windings in the motor! Top speed of the train is regulated automatically through calculating the gearing and weight ratios, and will pretty much stay the same no matter if it's going up a hill or loaded with passengers or not. (this however has been a problem in getting electric automobiles to keep up with 80+ mph interstate highway traffic and still achieve good range)

Actually, without resistors, they'll juast trip the substation or blow something up. On systems like the NYC subway, available fault current is easily 6 figures, running currents are easily 5 figures. Yes, that high(!). Balancing speed *is* a function of weight/grade/voltage. Older electrics like the old MP-54s and Lacawanna cars and the recently retired ACMUs, did in fact top out at different speeds depending on condiions. What's changed is that newer stuff has enough power to 'power through' all the way up to the maximum allowed speed. The ACMUs topped at around 60 - 70mph, even though the track was 80mph. They just didn't have the power to go faster.

Oh yes, the 'D' in class 'D doesn't stand for anything - it's just the designation that came after C (which is used in RF applications). It was developed I believe in the late 40's, as was PCM digital (yep - Bell Labs was showing that off then).

You can do it with tubes, too

 

[rickr]

Tubes or transistor? Which is best for an old console stereo? The 1982 Sansui is out. It would not fit into this console, and even if it did, would be too much power for this setup, with all four speakers in the same cabinet.
Besides, I could get a Magnavox tube amp plus the correct tuner that will fit this console perfectly for very little money.

 

[rickr]

.

Hey Ken,

I looked at the tuner and amp on the Astro Sonic solid state setup. It has two 50mfd35v caps, two 300mfd35v caps,four 500mfd15v caps, two 300mfd20v caps,three 100mfd10v caps,&two 250mfd10v caps. So all of those should be replaced?

What about the two 1500mfd35vdc "can type" caps? should those be replaced also?

Where should I go to obtain these? Seems like all one can get at Radio Shack is help with your cell phone these days...
Grangers perhaps?

Please let me know you guys. If I find out where to get all these, maybe I can get them at lunch tomorrow and install them on Saturday.
Then if I still am not satisfied with the transistor amp, I will still have time to snipe a tube setup next week.

Thanks again!

PS will show a couple pixs of my 1950's tube type (other) Magnavox now.

 

[rickr]

my other Magnavox

Is a hi-fi from the 1950's it lives in the basement rec room

 

[rickr]

.

tuner close up...

 

[rickr]

.

Record changer (not original) This had a junk BSR plastic changer in it from the 1970's. I replaced it with a late 1950's Collaro for Magnavox record changer. It had a rubber mat, but I changed it to the grey felt for a more vintage look.

 

[rickr]

Sorry....Forgot one thing...

whooops! Forgot to mention, none of the caps mentioned in the post about cap replacement is ceramic. The ones I mentioned for replacement are all electrolytic

Thanks!

 

[kenwashesmonday]

Best to change all the electrolytics. I don't remember if there are any plastic bumble bee / black beauty caps in there, but if there are they must go too.
Replace the cans with seperate caps under the chassis. Those little terminal strips to solder the parts to can be hard to find, if you need one I could send it.
Go to mouser.com for caps. They have no minimum.

Ken

http://www.mouser.com

 

[tolivac]

Amp wattages-Oh boy-For ealier units before CPC amplifier rating standards-it was a tough call.Some manufacturers didn't publish wattage ratings to be safe-Magnavox.And McIntosh Labs(early)even before CPC standards published the RMS rating of their amplifiers.And theirs could hold to it without overheating.The mcIntosh units were used a lot in the early days for broadcast and recording studio monitor amps.Recording studios and some on air studios played monitors LOUD.The amp had to take it and the speakers.Since tube amps clipped "softly" speakers weren't likely to be damaged.As far as the power goes-if you have a 15W tube amp and a 15W solid stater of the same power-just that 15W.Yes-some SS amps can run lower impedeance speakers-but be careful here-the output transistors are Drawing DOUBLE the current from the power supply-they could overheat.If the SS amp is shorted-the transistors will burn up immediately.with tube amps-a short generally will not harm them-but do do it.Whats bad for tube amps is an OPEN circuit on the output side-therefore DO NOT use speaker fuses with a tube amp-an open circuit for a tube amp could be fatal for the output tubes or transformer.An open circuit on a SS amp will not harm it.The output transistors will draw little or no current.
For "switching" or Class "D" amps-these are not new to AM and SW transmitter builders.These circuits have been used in such equipment for about 3 decades now.Yes a tube can run class "D"-in either Class "C" or "D" the device is actually acting as a switch.The tube or transistor conducts very heavily-than does not.(biased to "cutoff')This makes Class "D" amps very efficient-and does away with a second tube or transistor.also does away with output transformers.However the output filter-matcher network has to be CAREFULLY designed to give low distortion-and wide frequeuncy response.also the switching frequency is critical-to low and the amp has poor bandwidth and aliasing-the beating of high frequencies you want to amplify beating with the switching frequency of the amp-causing harmonics.In the case of broadcast transmitters you could say the switching modulator acts as a switching power supply of sorts.It supplies the High plate voltage for the RF amplifier and the audio modulating voltage.To modulate an AM transmitter 100% youy have to have amodulator that supplies at least 50% of the RF output power-IE 10Kw transmitter-the modulator has to gewnerate 5Kw of output power.In many AM transmitters I have worked onthey have conventional push-pull stages with transformer coupling-much like the output of a tube Hi-fi amp-couples the audio from the modulator to the RF PA stage-the PA stage acts as a "load" for the modulator amp.these contain large glass or ceramic metal tubes-usually of the same type as the RF stage.and they run as Class AB or Class B.In fact smaller tubes-like whats in hi-fi amps-drive the grids of the modulator tubes.The switching modulators-the low level switching stages are soilid state-and the switching modulator has only one power tube instead of two-cuts the cost-and is more efficient.Less heat to remove.and the one tube is cheaper to buy-station managers love that.but the downside of the switcher mods-is very high floating voltages-and sometimes poor raspy sound quality.Since modulatoion transformers are big,heavy and expensive-the switcher mod doesn't need them.But the Low pass filter cans be just as expensive.-but it is lighter.Of course-the filter in the AM transmitter has to pass DC-but in a Switcher amp for a speaker-does not-in fact the DC would burn out the speaker rather quickly.Oh-in modern train motor controllers-many of the resistors have been eliminated-the switching and VFD motor controllers don't need them for current limiting-only for braking.Therefore-less heat to remove.