Is it possible to replace certain octal tubes with equivalent miniature
in an older receiver and would there be an performance improvevment?

Just mainly looking to boost performance.
Any advice, thoughts, comments appreciated.

Thanks...Gil

wrote:
Is it possible to replace certain octal tubes with equivalent miniature
in an older receiver

For the most part, but it depends on the "certain" tubes.

and would there be an performance improvevment?

No, not really. If anything it would probably be a lot of work to get
things so the performance is not degraded.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

wrote:
Is it possible to replace certain octal tubes with equivalent miniature
in an older receiver

For the most part, but it depends on the "certain" tubes.

and would there be an performance improvevment?

No, not really. If anything it would probably be a lot of work to get
things so the performance is not degraded.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

In article .com,
writes:

Is it possible to replace certain octal tubes with equivalent miniature
in an older receiver and would there be an performance improvevment?

Just mainly looking to boost performance.
Any advice, thoughts, comments appreciated.

The answer is "it depends"...

There are miniature equivalents or near-equivalents of many metal tubes.
(AFAIK, all metal tubes are octals, btw). For example, the miniature 6AQ5 is a
very close equivalent to the 6V6, except the interelectrode capacitances are a
little different and the maximum ratings somewhat lower. If you can't get the
metals but can get or have the miniatures, such a substitution can be really
useful.

Performance improvement is more complicated. Development of metal receiving
tubes pretty much ended during WW2, and postwar development was almost all
aimed at miniatures. So you can find miniature receiving tubes with much better
characteristics. For example, about the best remote-cutoff pentode metal tube
you'll find is the 6SG7, which is pretty close to the miniature 6BA6 in
performance. Later miniature remote-cutoff pentodes such as the 6BZ6 and 6EH7
have more gain and less noise, and can really hop up an older receiver.

But you can't just substitute them and get a big improvement, in most cases.
The different capacitances can require realignment, the voltage/current
requirements are usually different, etc. Most of all, the higher-gain new tubes
may cause stability troubles. All of these difficulties can be overcome, of
course, but doing so requires a bit of redesign of the various stages.

There was a time when such tube substitutions were commonplace in ham gear,
because a lot of hams could better afford hopping up an old receiver rather
than buying a newer one. Nowadays, historical preservation is often the
deciding factor.

What receiver(s) are you trying to improve?

73 de Jim, N2EY

In article .com,
writes:

Is it possible to replace certain octal tubes with equivalent miniature
in an older receiver and would there be an performance improvevment?

Just mainly looking to boost performance.
Any advice, thoughts, comments appreciated.

The answer is "it depends"...

There are miniature equivalents or near-equivalents of many metal tubes.
(AFAIK, all metal tubes are octals, btw). For example, the miniature 6AQ5 is a
very close equivalent to the 6V6, except the interelectrode capacitances are a
little different and the maximum ratings somewhat lower. If you can't get the
metals but can get or have the miniatures, such a substitution can be really
useful.

Performance improvement is more complicated. Development of metal receiving
tubes pretty much ended during WW2, and postwar development was almost all
aimed at miniatures. So you can find miniature receiving tubes with much better
characteristics. For example, about the best remote-cutoff pentode metal tube
you'll find is the 6SG7, which is pretty close to the miniature 6BA6 in
performance. Later miniature remote-cutoff pentodes such as the 6BZ6 and 6EH7
have more gain and less noise, and can really hop up an older receiver.

But you can't just substitute them and get a big improvement, in most cases.
The different capacitances can require realignment, the voltage/current
requirements are usually different, etc. Most of all, the higher-gain new tubes
may cause stability troubles. All of these difficulties can be overcome, of
course, but doing so requires a bit of redesign of the various stages.

There was a time when such tube substitutions were commonplace in ham gear,
because a lot of hams could better afford hopping up an old receiver rather
than buying a newer one. Nowadays, historical preservation is often the
deciding factor.

What receiver(s) are you trying to improve?

73 de Jim, N2EY

I have to agree with the other posts and say that its probably not worth
the effort. If the primary reason for the effort is to improve
sensitivity, a tunable RF preamp (e.g.: Ameco PCLP) with a decent n.f.
will oft times work wonders. I use one of these in-line with the
antenna selector of receivers such as the RBS, RBM, BC-348, BC-312,
various older Hammarlunds and Hallicafters with excellent results on the
higher bands. One size fits all!!

wrote:
Is it possible to replace certain octal tubes with equivalent miniature
in an older receiver and would there be an performance improvevment?

Just mainly looking to boost performance.
Any advice, thoughts, comments appreciated.

Thanks...Gil

I have to agree with the other posts and say that its probably not worth
the effort. If the primary reason for the effort is to improve
sensitivity, a tunable RF preamp (e.g.: Ameco PCLP) with a decent n.f.
will oft times work wonders. I use one of these in-line with the
antenna selector of receivers such as the RBS, RBM, BC-348, BC-312,
various older Hammarlunds and Hallicafters with excellent results on the
higher bands. One size fits all!!

wrote:
Is it possible to replace certain octal tubes with equivalent miniature
in an older receiver and would there be an performance improvevment?

Just mainly looking to boost performance.
Any advice, thoughts, comments appreciated.

Thanks...Gil

My most recent project is making a replica receiver - but using octal tubes
to replace the original miniature one.

Wonder what would happen to my GPR-90 value if I spent about a month to
convert it to octal based equivalents?

Fortunately, other projects are more in front of that one.

Colin K7FM


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.783 / Virus Database: 529 - Release Date: 10/25/04

My most recent project is making a replica receiver - but using octal tubes
to replace the original miniature one.

Wonder what would happen to my GPR-90 value if I spent about a month to
convert it to octal based equivalents?

Fortunately, other projects are more in front of that one.

Colin K7FM


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.783 / Virus Database: 529 - Release Date: 10/25/04

In article et, "COLIN LAMB"
writes:

Wonder what would happen to my GPR-90 value if I spent about a month to
convert it to octal based equivalents?
Fortunately, other projects are more in front of that one.

"Fortunately" is right!
Tell you what, save some work -- you ship me the GPR-90 without the
ocnversion,a nd I'll pay you what it would be worth afterwards :-) :-) :-)
73, Mike K.

Oscar loves trash, but hates Spam! Delete him to reply to me.