Thread: 91 XG Modified
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Old 15-Jun-2020, 12:25 PM   #29
Sev
Member
 
Join Date: Jan 2016
Posts: 81
Quote:
Originally Posted by tripelo View Post
Yes, plus.

Channel Master and some other manufacturers have not provided accurate noise figure numbers.

Numbers often provided are quotes from transistor manufacturers specs.

There is more to noise figure than transistor specs, for example:

- The excellent input filtering of the 0264/0064 and other older CM preamps, contribute to the noise figure.
- The loss in the ferrite balun adds to the noise figure.



The VHF amplifier is a BFG198.

The first UHF transistor is a BFG67

(1st transistor is usually main active source of noise)

-------------------------

The 0064 & 0264 are good and reliable preamplifiers.

The design, except for input baluns, is virtually the same as for the old CM7778.

The old CM7778 was cloned to the RCA_TVPRAMP1R.

http://forum.tvfool.com/showpost.php...76&postcount=2


.
I assume both of the BFG components are on the back side of the board?
This image popped up on google.
A thread with you and Pete Higgins.
https://forum.tvfool.com/showthread.php?t=13530

Do you know of any alternative componets that would lower the noise figure. Or based on the design it is baked in?



One of the members a long time ago mentioned to me that the RCA was a clone of the 7778. The first preamp I picked up actually.

So based on Calveras's testing. The CM's and RCA's had a noise figure very similar to the Blonder Tongue Galaxy III's. Assuming that B.T. was being truthful about their noise levels.
I have come across a few B.T. 300ohm dual inputs with the 75ohm output but passed no them because there did not appear to be much love for them due to their advertised noise figures.

Any idea if those figures are actually accurate or not?

To clarify a statement back on post #14 you stated you removed the ferrite bead and replaced it with a half-wave loop on a Spartan?

OTAFAN posted an interesting idea concerning replacing the polarized caps with non polarized.

Thoughts?

Modding the board should not be very difficult. Though I would like to find another Spartan to test on.

Last edited by Sev; 15-Jun-2020 at 12:59 PM.
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