¿ªÔÆÌåÓý

ctrl + shift + ? for shortcuts
© 2025 Groups.io
  1. Ham-Amplifiers
  2. Messages
Single Messages Topics Expanded Polls

Re: Building my first amplifier. Where to start?

 

¿ªÔÆÌåÓý

If your 8k Ultra sags down to 4800 volts you have something wrong.? Possible weak AC line, or failed Oil caps.? I used a Fluke HV probe and mine sits at 5900 volts.? panel meter shows 6000.? ?At rated 5kw output it sags to 5500.?

The 8K has a very small power supply. Its only a 1 AMP CCA transformer with 2-amp surge.? It was designed for 5kw pep on SSB and no more than 1 amp plate current in Data modes. That is RIGHT IN the manual.? ?Its rated at 8k INPUT to the power supply.? NOT output.?

This is a good example of my exact point.? The amp will make 7000 plus pep with video all over the net showing this.? It does this on SSB with a 2 amp transformer That I can pick up and walk away with.




From: [email protected] <[email protected]> on behalf of Jim VE7RF via groups.io <jim.thom@...>
Sent: Wednesday, January 10, 2024 10:15 AM
To: [email protected] <[email protected]>
Subject: Re: [ham-amplifiers] Building my first amplifier. Where to start?
?
On Tue, Jan 9, 2024 at 11:15 PM, W7WRX wrote:
Its not hurting the tube.? You need to remember that this is Single side band with a duty cycle of 15 to 20 percent.? Even with heavy processor is not past 25%.??
?
What will the amp be used for???
?
This is a very common mistake made all over amplifier groups.?
?
Another one is Blower CFM and pressure.? All the time I see these guys saying you need X CFM or you need 300CFM!!!? That blower is to small....? I got advice from a guy that suggested I get a blower TWICE the size of the tube data sheet, Just for good measure.? LOL
?
?But those ratings are for 24/7 full power at rated Plate dissipation for 8000 hours.? A ham using SSB will never need anywhere near those ratings.? Even if you ran A digital mode you still would never need broad cast ratings.
?
Another one is transformer current.? If the amp is for Ham use it will not need the full rating of the tube spec sheet in transformer.? Ever.?
?
?Its comical people buying 175lb transformers only to use the amp on side band and never even pull HALF the current its capable of.?
?
It should be built for its intended?purpose.. If it is meant to run Data modes at high power with long operation of a contest, I get it... over build the thing. But most of the time, the amp is just going to be used on SSB with Data or CW less frequently.
?
?
C

The bigger plate xfmr typ results in less B+ sag on ssb / cw.? The 8K ultra sags from 5400 vdc, down to 4800 vdc.? Mine sags just 50 vdc.? ?5500 down to 5450 vdc.? The ebm papst blowers I got a while back (EC type) have variable speed on em....via an external 10 k pot.? I can drop the rpm in 1/2.? You are correct though, on ssb, less air required....and on extended RX, even less air required.?

?

On the dc input side, my average plate current is exactly 1/2 of key down cxr.? This is with ssb and a lot of processing.? I call that a 50% duty cycle...on the input side.? On the output side, the average PO is only 29% of the pep out.?

?

I have yet to experiment with data /? FT-8 modes.? FT-8 destroys typ amplifiers.? I factored that in, and designed it, so slightly reduced ratings are used on data modes.?
Join [email protected] to automatically receive all group messages.