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Author Topic: Ameco preamp  (Read 329 times)

EI5GUB

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Ameco preamp
« on: January 04, 2023, 06:16:37 AM »

Hi I have an Ameco preamp here that I got from America yrs ago,its the one with the 2 small valves,I need a power supply for it that does 150volts and 6.3volts for the heaters bearing in mind that our household voltage in Ireland is 220v,any ideas please.
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WB6BYU

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Re: Ameco preamp
« Reply #1 on: January 04, 2023, 07:51:14 AM »

The standard solution at the time was to use the transformer
from a junked valve television set or other equipment
(although the cheap table radios in the US often didn't
have transformers - they rectified the mains voltage for
the B+, and wired tubes in series across the mains - this
required an insulated cabinet for safety, and is less of
a good idea with 220V mains than our lower voltage!)

This project shows an example power supply, with the three
tube filaments connected across the mains, along with a
series resistor, although the B+ may need to be dropped
in your case.


If you can find a transformer that delivers a reasonable
lower voltage, then I've seen designs using a diode
voltage multiplier from that winding to get the B+. 
You might have to wire the two valve filaments in
series to run on 12.6V, or use a switching DC/DC
converter (the valves will run on DC rather than AC).

Back when the unit was manufactured, some
receivers had a power jack on the back to allow
the internal power supply voltages to be used for
other projects.  My old Heathkit AR-3 had one.


So a general approach these days is to see what
you can find for a transformer, and design the power
supply around that.  I can often find plug-in AC
transformers at 16V or 24V that are designed to power
older alarm or telephone systems, like this one.
You can then use a diode multiplier as needed to get
your B+, and a dropping resistor or regulator to get
the filament voltage.  If you find one with 10V center
tapped, you can use half the winding for the filament.

If you can find a suitable transformer with a 6V winding
for the filaments, you can use an American unit with a
120VAC primary in reverse to step the 6.3VAC back up
for your B+.

And, depending on the transformer style, you may be
able to remove the secondary windings and add your own.
That's probably most practical if the secondary has a high
enough voltage that you can just remove turns, then add
another secondary (with fewer turns) for the filaments.



WA3SKN

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Re: Ameco preamp
« Reply #2 on: January 04, 2023, 08:20:56 AM »

They were "low noise preamps" of the time.
However, there are much better solutions now... technology has changed.
You might want a lower noise, cheaper solution.

-Mike.
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N2LXM

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Re: Ameco preamp
« Reply #3 on: January 04, 2023, 08:26:27 AM »

Here is a link to paperwork I had uploaded to the B.A.M.A. site. It shows what voltage levels are needed. " http://bama.edebris.com/download/ameco/cn50/Ameco%20Opr.%20Guide%20Models%20CN-50,%20CN-144,%20CN-22002252014_0000.pdf "
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W9GB

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Re: Ameco preamp
« Reply #4 on: January 04, 2023, 05:04:52 PM »

The Ameco Converters used four (4) vacuum tubes.
N2LXM supplied those documents.
==
Quote from: EI5GUB
I have an Ameco preamp, that I got from America years  ago.  It is the one with the 2 small valves.
I need a power supply for it.
Ameco made a number of RF Pre-Amplifiers (PT, PT-2, PT-3)

The Ameco Pre-Amplifier model PT documents are at BAMA Mirror.
https://bama.edebris.com/manuals/ameco/

The Ameco model PT pre-amplifier used the 6EH7 vacuum tube and
operated from 117 VAC, 60 Hz (North America)

Ameco model PT Pre-Amp Manual
https://bama.edebris.com/download/ameco/pt/AMECO%20PT%20Preamp%20(Tube%20Type)%20Manual.pdf

Ameco model PT Pre-Amp Schematic
https://bama.edebris.com/download/ameco/pt/AMECO%20PT%20Preamp%20(Tube%20Type)%20Schematic.pdf
« Last Edit: January 04, 2023, 05:16:38 PM by W9GB »
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EI5GUB

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Re: Ameco preamp
« Reply #5 on: January 08, 2023, 11:35:06 AM »

Hi thanks to all who replied to my post and sorry for the long delay in replying,im just busy with work after Xmas etc,im afraid transformers of that nature are not easy to come by here in EI land so will just put preamp back in the press for another few years,i just wanted a preamp for the Yaesu FRG7000 down in the kitchen to boost signals a bit,its fed with a 60 ft long wire antenna at 40ft high and has to radial wires 15 feet long buried under the ground,anyway thanks again to all and good DX in 2023

73s de Richard EI5GUB
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WA3SKN

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Re: Ameco preamp
« Reply #6 on: January 09, 2023, 06:02:15 AM »

A pre-amp may not be your best solution.
The FRG7000 has both a pre-selector and an attenuator.  My understanding is that noise from the digital display would get into the local audio circuits, and there was a way to turn off the digital display to negate this.  You might want to verify that there is a lack of sensitivity before adding a pre-amp.

-Mike.
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KG4RUL

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Re: Ameco preamp
« Reply #7 on: January 09, 2023, 06:18:52 AM »

I think it is great that you want to get the preamp working again.  Yes, there are better solutions now but, if you have a vintage station, old school is more relevant.  Look on eBAY or AliExpress for suitable transformers.
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N8YX

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Re: Ameco preamp
« Reply #8 on: January 09, 2023, 07:31:37 AM »

I'd watch the auction site for an active preselector (has an internal preamp). Palomar and several others made them.
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N7EKU

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Re: Ameco preamp
« Reply #9 on: January 09, 2023, 05:10:04 PM »

Hi,

Wouldn't it be OK to just rectify and regulate your line voltage?  I'm sure there are high voltage three  terminal voltage regulators available for this.  Maybe there are safety aspects about this that I am not aware of though. I don't imagine you need a lot of current?

For the filaments, I would just use a doorbell transformer or something like that, if you can't find a filament transformer for your line voltage.

73
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Mark -- N7EKU/VE3

WB6BYU

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Re: Ameco preamp
« Reply #10 on: January 09, 2023, 06:41:12 PM »

Quote from: N7EKU

Wouldn't it be OK to just rectify and regulate your line voltage?...



This was popular for the old AC/DC tube sets in the US, but the
higher 220V mains voltage in Europe significantly increases the
hazards of that approach.  Especially for equipment that was not
originally designed for a "hot" chassis.

Any series resistor or regulator delivering 300 mA for the filaments
is going to need to dissipate over 50 watts.

In this case, the two most likely solutions would be (1) use a
modern switching power supply to generate the required
voltages, many of which will run from 100 - 250 volts, or
(2) see whatever sorts of transformers are available, and design
a supply to use them.
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