Re: 6SN7 amp initial report


"Stephen Cowell" <scowell@xxxxxxxxxxxxx> wrote in message
news:7PDjl.22339$ZP4.18941@xxxxxxxxxxxxxxxxxxxxxxx

"Phil S." <psymonds@xxxxxxxxxxx> wrote
"jh" <jh@xxxxxx> wrote
...

With the intermittent 6SN7, if pressing the glass in to the base helps,
you might try to carefully resolder the pins. I've revived more than one
tube...
Yes, pressing glass from the top makes it work. I don't understand
what's involved here. I need to remove the base? How is that done
without breaking it?

This is a job for a solder pot... or you can try sucking
the solder out one pin at a time. I'd toss the tube, myself.
You should find a broken wire when you get the base off...
if it's broken at the glass, good luck.... actually, good luck
anyway, it's fiendishly hard to fix (how do you keep a soldered
wire together *inside* the pin when soldering?)

With the distortion analysis (tubes vs transformers), i guess it's
really time for a scope now. My first scope (that i really miss) was an
old Tek 561? (i'm not at home to look what it exactly was) Two trace,
differential input, max 20MHz. It served me really well for years, Real
big mother, enough heat to warm a room, but great low level results,
perfect for audio work. Really tough regarding abuse - applying 550V DC
while in mV settings etc. I only realized what i lost, when I had the
replacement. Also a tek, but a fairly recent one (2225 or something like
that).
I bet they are dirt cheap, because they are much too slow for digital
analysis. I bought mine in 93 for 120DM then (~60$) it was from an old
university stock.

The language of scopes is confusing to me. This small explanation is
helpful. You're saying I can get the kind that no one wants anymore.

Jochen is describing a tube scope... all Tek 500 series. They are giant-
sized, heavy, and delicate. The only reason to get one is if a.) it
works
and b.) it's right in front of you. Never ship one, it'll arrive full of
broken
glass. I have four or five carcasses of these.

I started to watch auctions on eBay to see how the bids end. As for
brands, you and Steve Cowell like Tek. What else is OK? HP? BK? I
thought it would be nice to get a smaller "desktop" model.

Yes, giant scopes are great for Frankenstein labs... OTOH, those
LCD handheld scopes are to be avoided as well... frustratingly
slow and also delicate around HV.

What's up with probes? They seem expensive.

They are, for good reason... a shitty scope probe will
make your life miserable. Your best bet is to get one
(or several!) with the scope you buy; another reason
to buy a good, used scope instead of a new, cheap
one. Don't get a tube scope unless you want to maintain
it yourself, and can envision enjoying it. A simple 20mHz
single-trace Heathkit, B&K, etc would be great for amp
work... dual-trace, delay, storage, etc are all icing on the
cake. I've been very happy with my 453 Tek, it's a rock.

Watch for burned phosphor... you'll see it as a mark
on the display that doesn't go away when the power
is off. This is permanent damage and significantly
reduces the value of the instrument.

OTOH, you can get plenty of scope for $25 at
a hamfest... watch for hamfests in your area.
Plus, you can buy from a grumpy, white, old
man! Bonus!
__
Steve
.


Steve,
This grumpy old white man at the hamfest seems like the best advice. I
guess you don't have anthing here to help me explain to my wife why I'm
rising uncharacateristically early, before dawn on a Saturday, to go where?
To get what? This may be more of an obstacle than money.

I once showed up at a hamfest at about 11:00AM. It was all but over.
Phil


.

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