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Need a full compliment of Tubes for a Scott 340-B

M

mcdonougha

Member
I recently tested the tubes in my Scott 340-B receiver and found out they were all on their way out or dead. I know ebay can be a good source for tubes but i dont want to be going through several different vendors/people to get what i need. Does anyone know a good place to get these tubes?

I've heard the new tubes made today aren't great, so i guess NOS tubes are what i prefer.


Here's what i need
18 Tubes:

10-tube, Amplifier section:
(4) 12AX7 - preamps
(2) 6U8/6GH8
(Split-load phase inverters)
(4) 7591 outputs

5-tube, FM Tuner section:
(1) 6BS8/6BQ7 - FM RF amp
(1) 6U8 FM mixer
(2) 6AU6
(1) 6HS6

3-tube, FM MPX section:
(1) 12AT7
(1) 6KE8
(1) 12AX7
 
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bear in mind that changing any of the tuner tubes will almost certainly require realignmment of the receiver.

Sometimes it's best to stick with tired tubes.

What's wrong with all of those tubes?? Usually the small signal tubes last a long, long time (virtually forever in vintage hifi gear).
 
Saratoga48 said:
I'd test the tester, no way should all those tubes be bad.
Click to expand...

I second this! Find someone with another tester and try the tubes there if there's no way of calibrating the tester you have.

Also, while working on an old Scott 222c once, the 6U8 tubes, which were original, and telefunkens, tested at only one point above minimum on the good TV-7 A/U tester at work. Gordon kept feeding me various combinations of new and NOS 6GH8 tubes to try in the amp, even a couple of strong NOS Amperex tubes, but NONE of them came even close to sounding as good as those "dead" Telefunkens, so back in they went. Point being, on a good, high quality tester, "good" means "good"!

Is the receiver playing badly?
 
I fully agree with the previous comments regarding the reliability of the
tube tester. If you could get your hands on a few New Old Stock tubes
of the less costly types used in your receiver, for instance the 12AT7
or 6AU6, you could try them in the tester and see what you get.

Also, assuming that many of your original tubes have really gone bad,
you must realize that this is almost certainly the case also for many of
the passive components in your receiver (resistors, electrolytic capacitors,
etc.). A thorough restoration might be in order. Good luck.
 
Well I did have them retested at a friends place and some of the tubes are bad and some are on their way out. All in all the receiver sounds great, i just want to replace them to prevent any damage.
 
mcdonougha said:
Well I did have them retested at a friends place and some of the tubes are bad and some are on their way out. All in all the receiver sounds great, i just want to replace them to prevent any damage.
Click to expand...

Well, damage prevention is generally done through rebuilding the amp by changing out the old Electrolytic can caps, the selenium rectifier, replacing the old white Ceracaps, resistors gone out of spec, cleaning tube sockets, setting the bias and balance to proper levels, etc.

If you've already done this, great. If not. . . it's definitely time to be done.

I'd also like to point out that you omitted the most critical tube to the performance of the amp. . .

The GZ34/5AR4.

I don't know why people never list that one, because without it everything else just doesn't matter. (My opinion, of course)

I recommend a Mullard made, fat base GZ34; between 1958-1961. They're nearly as good as the metal base Mullards made between 1954-1957. They only cost about 1/5 to 1/4 of the metal base tube's price, and they generally last for many years.

But, perhaps you already have a Mullard in there now, and it tests out strong and balanced.

Oh. . . if you plan to toss those Telefunken 12AX7/ECC83's and Westinghouse 7591's into the trash, you can send them to me. :)

. . Falcon
 
Output tubes may be worn out but it is unlikely that all the small tubes are. Get the unit restored if it isn't already. The 340B is a fantastic receiver, one of my favorite pieces of vintage gear. EH7591's have been reliable in my unit so far.
 
1) The real test of a tube is whether it works in the circuit.

2) They don't make most tubes anymore, so if you replace something, keep the weak one.

3) I can't think of a tube that will really damage the unit if it goes bad. Unless it dead shorts - but you can't predict that from output power.
 
toxcrusadr said:
1) The real test of a tube is whether it works in the circuit.

2) They don't make most tubes anymore, so if you replace something, keep the weak one.

3) I can't think of a tube that will really damage the unit if it goes bad. Unless it dead shorts - but you can't predict that from output power.
Click to expand...

2) Well, actually most hi-fi tubes are readily available, NOS or new production. Most, not all.

3) The output tubes can indeed do damage (rectifiers, too) when they go. In, e.g., a fixed bias Fisher receiver, the addition of cathode resistors can act as fuses to help protect the output transformer from an output tube short -- and it can, and does, happen. Some of the new production 7591s have been problematic.
 
mcdonougha said:
I recently tested the tubes in my Scott 340-B receiver and found out they were all on their way out or dead. I know ebay can be a good source for tubes but i dont want to be going through several different vendors/people to get what i need. Does anyone know a good place to get these tubes?

I've heard the new tubes made today aren't great, so i guess NOS tubes are what i prefer.


Here's what i need
18 Tubes:

10-tube, Amplifier section:
(4) 12AX7 - preamps
(2) 6U8/6GH8
(Split-load phase inverters)
(4) 7591 outputs

5-tube, FM Tuner section:
(1) 6BS8/6BQ7 - FM RF amp
(1) 6U8 FM mixer
(2) 6AU6
(1) 6HS6

3-tube, FM MPX section:
(1) 12AT7
(1) 6KE8
(1) 12AX7
Click to expand...


I'd have to question the accuracy of the tube tester used... I have never had all tubes in a FM receiver test weak or bad. In fact the reverse is almost always true. Many times they might require a set of output tubes and then a souple others at most.

In the 340B usually these would be the most likely and usually not all of them.

Amplifier section:
(2) 6U8/6GH8
(Split-load phase inverters)
(4) 7591 outputs

FM Tuner section:
(1) 6BS8/6BQ7 - FM RF amp
(1) 6U8 FM mixer
(1) 6HS6

FM MPX section:

(1) 6KE8
 
mhardy6647 said:
2) Well, actually most hi-fi tubes are readily available, NOS or new production. Most, not all.

3) The output tubes can indeed do damage (rectifiers, too) when they go. In, e.g., a fixed bias Fisher receiver, the addition of cathode resistors can act as fuses to help protect the output transformer from an output tube short -- and it can, and does, happen. Some of the new production 7591s have been problematic.
Click to expand...

Coming from more of the antique radio field, I probably shouldn't talk too much about amps. The output iron is certainly cheap for radios! But my point in #3 was that just seeing that a tube is weak is no predictor that it is going to short or damage the unit.

As far as #2, I was trying to prevent the discarding of possibly weak but admittedly working tubes as a matter of principle. Frugality is my middle name. Heck, half my tube stash are used ones that repair guys probably replaced just so they could sell the customer a tube.
 
I do agree with you, by the bye!

The small signal tubes are probably all fine. I'll take all the 12AX7s from that 340B if the OP doesn't want 'em!

On the other hand, it is possible that the receiver was run 24/7 for years (decades) and really is worn out, tubes and all.
 
Well i was talking with my dads brother and he said when they did have the receiver in use, it was used 24/7 for many many years.

But it also sat in a basement for at least 10 years
 
Regardless of the fact that there could be tester issues.........Antique Electronic Supply has alot of tubes. Prolly not all on the list....but alot. http://www.tubesandmore.com/

This is the second time i have name dropped these guys. If this keeps up I am going to have to ask for payment in the form of Tubes!!!!!!!!!!!!!!
 
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