[R-390] Role of the 3TF7 in PTO frequency changes

[sigmapert]

Hi Roger,
THX for your suggestions.
As far as I remember a huge number of post have dealt with 3TF7
substitutes of all sorts. Most of them tried to improve current
regulation of the filament supply.

It has shown by Dallas and me that voltage regulation is the better
alternative to achieve constant VFO frequency when power line voltage
changes. Similar to the perfect regulation of B+ using constant
voltage devices (R-390A: 0A2, R-390: 2 x 5651) constant voltage supply
of the filaments leads to perfect results. Why go back?

Besides the the better regulation of my replacement device power
dissipation is reduced substantially. Touch the 3TF7 with your finger
after touching the solid state device for several minutes and count
the seconds you can grip the 3TF7 (LoL).

Now a comment to the replacement of original parts with new ones. I
would e.g. NEVER replace original capacitors with orange drops. In my
eyes they are oversized and look unaesthetically (the orange drop
lovers will kill me). If possible I'd avoid any soldering in the
radio. That was the 'ultima ratio' when designing the 3TF7
replacement. But if a replacement (even a solid state device, Hallo
Heinz Breuer) fits well into the look of the radio I see no problem to
install it. The 3TF7 replacement with the medium size IERC tube shield
installed (http://schmid-mainz.de/Flyer.pdf) to my feeling isn't
recognized as a foreign body even by the purist.

Currently I'm experimenting with solid state replacements of the two
6082 tubes in the R-390 non A. These beasts cook the radio. As I stated
above I'd never tolerate to do any soldering in the radio. I've good
evidence to succeed in the design of a direct plug-in replacement of
small size and low power dissipation using most recent switching
voltage regulators.

So Roger, I've plenty of projects to deal with. Voltage regulator
issues was a deviation from my long-time project 'Measurement and
alignment of PTOs'. I have built a jig that uses an absolute rotary
encoder to quantify the rotary angle of PTOs with high precision
together with the related output frequency of the PTO. Here a picture
of my setup. (http://schmid-mainz.de/Jig.jpg)
For this subject I'm preparing a manuscript for 'Electric Radio'.

Regards to you and all list members. I hope you like my work and my
enthusiasm for our beloved R-390(A) radios.

> Kurt,

> Will you please conduct two more experiments and report the results for us.

> Test 1. Short the ballast tube out and install 12BA6's in the BFO and VFO.

> Test 2. Use 5749's in the VFO and PTO and use a 12BY7 as a ballast tube.

> The question is, does the ballast tube really regulate the current short
> term and long term better than lower filament current of the 12BA6's or any
> other filament at .6 amps.

> I see the argument for the ballast tube smoothing short changes when the
> receivers were run off generator power. Also the ballast would smooth line
> transient from devices being switched on or off.  I do not see any long term
> regulation as the line voltage drifts several volts do to power line sag as
> the neighborhood changed demand during the day.

> Thanks

> Roger Ruszkowski
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-- 
Mit freundlichen Grüßen
sigmapert
mailto:sigmapert at gmx.de