[R-390] Off Topic - Transistor R390A sounding good.

Cecil Acuff chacuff at cableone.net
Sat Jan 1 15:21:18 EST 2005 

Hey Guys!

Well I can't speak to the latest of the audio hype but I have been in and 
out of the audio business over the years and dabble in the tube guitar amp 
area as well and can tell you there are differences in tubes.  In the guitar 
world tubes are used a little differently than in the rest of the world. 
Distortion is desired at times and how a tube handles being over driven has 
a lot to do with it's sound.  As was mentioned by another poster, most 
guitar players who are familiar with tube amps can pick the desirable tubes 
by ear.  What comes of that is that consistently what sounds good turns out 
to be certain brands in certain tube numbers.  So those brands are sought 
after as a somewhat general assurance that the desired sound will be 
achieved.  That's not to say that certain run of the mill tubes won't at 
times sound just as good but they don't consistently sound that way.

How and when a tube breaks into distortion and what type of distortion is 
delivered makes all the difference.  Most of the old Blues music that was 
recorded many years ago was done on old Fender Tweed amps and that sound is 
sought after today and hard to duplicate.  That's why 12AX7's, 12AU7's, 
6V6's etc of the right brand names go at a premium.  If you have European 
varieties of those they seem to be the most sought after.  Especially 
Telefunken and Mullard...

Now those same tubes used the way we use them in radio gear probably won't 
sound much different than a half used up (soft in the guitar world) GE.  So 
we are lucky we can get away with using just about anything.  I agree that 
maybe the RF/IF amp tubes would make the most difference to hand select.

In the audio world there are some tubes that sound more musical than 
others...I guess it's got to do with how the tube handles harmonics, 
overtones and transients which music is full of.  Beyond that...things like 
silver plated this's and gold plated that's....oxygen free wire...I think 
are more like the endless array of fishing lures...they lure more fisherman 
than fish.

I can say we used to have a display set up for Monster Cable speaker wire 
where there was 50' of what most folks used...something like 14ga zip cord 
and 50' of the Monster Cable speaker wire with a switch on one channel of 
nice stereo system and one could tell a MAJOR difference between the 
two...in level and low frequency audio quality.  Sold a lot of wire that 
way...one could quantify the difference!

Happy New Year!

Cecil...
----- Original Message ----- 
From: "David C. Hallam" <dhallam at rapidsys.com>
To: "R-390 HF Receiver List" <r-390 at mailman.qth.net>
Sent: Saturday, January 01, 2005 12:36 PM
Subject: RE: [R-390] Off Topic - Transistor R390A sounding good.


> Along these lines, can anyone explain for me why the audio people are
> willing to pay prices that approach or exceed $100 for specific tubes that
> are versions of garden variety tubes, i.e., 12AX7, 12AU7, 6SN7, etc.  What
> was done to these tubes that make them special or is it just the oxygen 
> free
> copper speaker wire all over again?
>
> David C. Hallam
> KC2JD
>
> -----Original Message-----
> From: r-390-bounces at mailman.qth.net 
> [mailto:r-390-bounces at mailman.qth.net]On
> Behalf Of Bob Camp
> Sent: Saturday, January 01, 2005 1:15 PM
> To: Charles B; R-390 HF Receiver List
> Subject: Re: [R-390] Off Topic - Transistor R390A sounding good.
>
> Hi
>
> One of the more interesting mysteries of the world is the enormous
> number of transistor part numbers out there compared to the number of
> tubes. If you look at a tube manual from the R390 era you will find
> roughly 1/100 the number of tubes compared to the number of transistors
> and diodes in an equivalent solid state book these days.
>
> We don't worry to much about a particular brand of tubes in the 390 but
> the audio guys go a bit nuts on specific manufacturers of "classic"
> tubes. As far as I can see the R390 approach (don't sweat it) works
> just fine except when you have a tube that's just plain bad. I have
> never seen a problem that always happens with a specific brand of tube
> in a 390.
>
> If you look in your 390 there are a bunch of fundamentally different
> tubes in it. You are not going to swap a dual triode for a pentode and
> have much success. Even if you stick to triodes they come in a wide
> variety of bias and gain setups.
>
> Bipolar transistors are different. You have two basic flavors NPN and
> PNP. Provided you don't run to much power, current or voltage do their
> thing ok. At a given current level the gain of most of them is very
> similar in a normal circuit.
>
> If you already have a bag full of diodes or transistors, try plugging
> one in and see what happens. It just may work and save you a major
> hassle.
>
> The Lankford SSB mod on the 390A is an very good example of this. There
> are probably thousands of diode part numbers that will work just fine
> in the circuit. They are easier to find by body style than by part
> number. If the diode looks like it will work it probably will.
>
> So if transistors are more like each other than tubes - why so many
> transistor types?
>
> Marketing rules ....
>
>
>        Take Care!
>
>                Bob Camp
>                KB8TQ
>
>
>
> On Jan 1, 2005, at 7:29 AM, Charles B wrote:
>
>> Hi all,
>> My R-390A is sounding good lately.
>>
>>
>> I don't know where to go for this info, so I am checking here?  I need
>> to replace a transistor.  I have gone to the
>> electronics store in West Palm Beach and they can't find it?
>> I checked with a source here on the web and it's not listed
>> in their catalog.  Anyway, if anyone could take a look
>> at the following number and let me know if they can
>> cross reference it, I'd appreciate it?  You can
>> get me off group at my email address of:
>>
>> ka4prf at us-it.net
>>
>> The transistor's number is     MPS 6530
>> I think the case has a large "E" on it?  The
>> resistor is an NPN type. O18 case
>> Thanks
>>
>> Chuck
>>
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