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Old 7th May 2004, 03:07 PM   #1
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A resident that lives at my property just gave me an old tube radio and amp that he said came out of a 1962 sears console (he ripped it apart but that is what some drugs will do to you??) is there anything that i can do with it? the amp looks in good shape and if i wire the amp and stereo up together it all works the amp is using 4 6bq5 and two 12ax7a is there a way i could just use the amp and ditch the stereo. they are two seperate pieces wish i had a diagram or something also how many watts do you think this is pushing? any help would help as i new to tubes
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Old 7th May 2004, 04:57 PM   #2
Morse is offline Morse  United States
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Hi cqboling;

>>>...is there a way i could just use the amp and ditch the stereo...<<<

???

Do you mean "use the amp and not the radio tuner?" Personally, I'd keep the radio section, since a properly working valve type radio generally sounds better than the garbage that's in modern "hifi" receivers.

As far as the amp is concerned, 4x 6BQ5 spells "stereo push pull", which for a 6BQ5 means on the order of 11 to 15 watts (actual power out depends on the operating point, or how "hard" the valves are being run), though it could be as high as 17 watts rms per channel. Those are REAL rms watts, rather than the phoney baloney ones that many manufacturers today are advertising.

My own 2 pence is: 1. keep all of it, 2. replace/repair/renew (have someone else do it if you lack the tech skills) any parts that are failing (like 42 year old electrolytic PS caps), and 3. prepare to be very happy with the sound. You would have to spend several hundred dollars for a pp 6BQ5 amp, and you got one free - along with a tuner!

Good luck and all the best,
Morse
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Old 7th May 2004, 05:15 PM   #3
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Morse beat me to the punch. I 2nd his recommendations. Replacing ALL electrolytic capacitors is MANDATORY. Electrolytic caps. physically dry out over time.

Look the units over carefully for markings. There should be model info on them. Obtaining schematics should not be too difficult once the models are determined.

If the equipment doesn't have the capability to accept an additional source, like a CDP, constructing a switch box that sits between the tuner and the amp is a simple enough project.

As Morse indicated, the Watts are genuine and you can use all of them. Tube amps compress before they hard clip. So, your tweeters are spared.
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Old 7th May 2004, 05:58 PM   #4
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Stereo PP 6BQ5 amps are fairly rare -- amongst my collection (probably approaching 75 amps now) i have some monos, but no stereo ones -- i did have a 4 channel one out of a Leslie, but i flipped that. That it actually works without any hum is quite rare in my experience -- i have 2 so far that i can actually use (PP 6BM8 and stereo ELL80).

Unlike morse, i see no reason to keep the radio section -- i've not found one of these that works decent, and the wiring is usually a mess.

The amp chassis has 4 x 6BQ5 + 2 12AX7s? That is the appropriate tube complement for a stereo power-amp (or even integrated).

As said, the caps will need to be replaced, and it is also likely that many of the old carbon resistors no longer have the same value.

1st thing to do, if you can't find a schematic, is to trace out one. This will give you an idea of where everything is.... and what you clip out.

When you remove the load from the tubes in the radio section, your volages will climb abit, so you need to measure what they should be before you start clipping, and after you may need to increase the size of a dropping resistor, or just add another CR section right after the rectifier (tube or SS rectification?)

dave
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Old 7th May 2004, 11:00 PM   #5
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well i guess i will just have to map it out myself on paper. should i replace the old wire with new as i am replacing resistors and caps? and does anyone have a link for the color code system used on the resistors it would save me alot of time thanks
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Old 8th May 2004, 01:20 AM   #6
Morse is offline Morse  United States
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Hi CQBoling;

Black = 0
Brown = 1
Red = 2
Orange = 3
Yellow = 4
Green = 5
Blue = 6
Purple = 7
Gray = 8
White = 9

Multiplier band:
Same codes as above PLUS:
Gold = x.1
Silver = x.01
Black is read as "times 10 to the 0 power" which means "times 1"

Tolerance:

None stated = +/-20%
Silver = +/-10%
Gold = +/-5%

Read it as follows:

First band = first digit
Second band = second digit
Third band = multiplier given as a power of 10 (in other words, multiply the number given in the first two digits by 10 to the {colour band} power).
Fourth band (if present) = tolerance band

Ex:

RED/RED/YELLOW/GOLD = 22x10^4 = 220,000 ohms or 220k ohms, +/-5% of stated value.

Brown/Black/Black/Gold = 10x10^0 = 10 ohms+/-5%

There are also resistors with up to an extra 2 bands. If there is an extra band AFTER the tolerance band that is YELLOW, it means "fire resistant". If there is an extra band BEFORE the tolerance band, use THREE "digit" bands FOLLOWED BY the "multiplier" band. Generally resistors with 3 digit bands will be +/-1% (brown) or +/-2% (red).

Given the era of your amp, the resistors are carbon comps, probably +/-10% and +/-20%.

Now for the inevitable question: "how do I know which band is FIRST?" Ans: experience. There are clues - a tolerance band of gold or silver is a dead giveaway. Also, certain "standard" values of digits (like 10, 15, 18, 22, 27, 33, 47, etc) occur regularly. Thus if you see "BROWN/GREEN/RED" you can be fairly sure it's 1500 ohms (15x10^2) +/-20% and not 250 ohms (25x10^1) +/-20%, since 250 is not a "common" value (please note that I did NOT claim there are NO 250 ohm resistors in existance - it's just that they are UNCOMMON, whereas 1500 ohm resistors are VERY COMMON). When in doubt, ALWAYS check things with a DMM.

Good luck and all the best,
Morse
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Old 8th May 2004, 07:35 AM   #7
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Quote:
Originally posted by cqboling
should i replace the old wire with new as i am replacing resistors and caps?
You might as well... 30 guage wire-wrap-wire works good, 24 g plenum grade ethernet strands is easier to work with.

For resistor values Danny Goodman has written a javascript program that makes it easy.

A copy resides here. Being javascript it will be flakey in some browsers (ie iCab -- works fine in Safari thou)

dave
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Old 22nd May 2004, 04:44 PM   #8
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well i finished up and i must say it is a great little amp goes way louder than i would want to listen, my speakers are fairly efficient. I did have some problems with hum but it was just stupidity on my part both channels work great seperation is good especially when the price was almost free...when i get a digital camera i will post some pics thanks for all your help
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