Chinese 15W Amp

[reverend]

chinese-15w.jpg

Has anyone played with one of these Chinese so-called '15 Watt' amplifiers? I've mucked about with it, but the best I can get is around 10 Watts. Of course, I never really expected it to deliver the full 15 Watts, but also assumed that the device used would be an RD15HVF1 which should loaf along at 15 Watts, however it clearly isn't. My guess is that it might just be an RD06HVF1 which can squeeze 10-12 Watts.

Rev

[radium98]

what is the bias voltage measured ?

[teckniqs]

You may be able to get a bit more by tuning (opening) some of the coils, I expect it would probably work better at the bottom of band looking at the number of turns.

[Albert H]

That "filter" won't do much - the coils will couple to each other......

[Krakatoa]

Maybe you can replace the transistor with the real deal and see if you can get the 15w.
Otherwise, we are talking about chinese watts, they say 15w and in reality you get 7.5.
You should have bought a 30w unit and you'd get the needed 15w.

[reverend]

Thanks for all the useful feedback.

You may be able to get a bit more by tuning (opening) some of the coils, I expect it would probably work better at the bottom of band looking at the number of turns.

I've re-capped the output filter so that I know the values are about correct, but that made no difference, nor did mucking about with the coils either.

That "filter" won't do much - the coils will couple to each other...

I know, what a dreadful design in that respect

Maybe you can replace the transistor with the real deal and see if you can get the 15w. Otherwise, we are talking about chinese watts, they say 15w and in reality you get 7.5. You should have bought a 30w unit and you'd get the needed 15w.

I never really expected 15 Watts, I just bought it to play around with. I've got a so-called '45 Watt' Chinese amp which cost about a tenner and that manages nearly 10 Watts I'll probably do as you suggest and put the correct FET in there and see what happens. My guess is that they've taken a 15W PCB design and just put a 6W transistor in it, which is why they've rubbed the part number off the front of the device

[rigmo]

chinese-15w.jpg

Do you have link?

[yellowbeard]

https://www.ebay.com/itm/124312996691?h ... SwJBlayLWi
Don't do it! Dutch shit is 1/2 the price and it works.
https://www.amateurradioshop.nl/webshop ... lator.html

[teckniqs]

https://www.ebay.com/itm/124312996691?h ... SwJBlayLWi
Don't do it!

"operating current of 10A"

[reverend]

I can 100% confirm that these devices are a pile of turd. With the original transistor in place, they do provide about 8-10W out with a couple of component changes. With a replacement RD15HVF1, they just hoot at about 170 MHz, or produce 10 Watts of wideband crud. If you didn't have a spectrum analyser but were just measuring the output power you might not notice! Operating current is about 2.5 Amps. The input matching is dreadful too. Waste of a tenner (saw one cheap on Aliexpress) that could have been far better spent on beer.

[Albert H]

Weirdly, I saw a Chinese "20 Watt" amplifier board that was nicely laid out, included a FET that would actually achieve the rated power (and a bit more), had a reasonably good output filter, and only needed about 300mW of drive. It had to be run at 18V to get the 20 Watts, but it worked OK and was clean. These came from a factory in Kowloon (where Uniden used to get boards made), and cost around £20 each, or less if you bought a boxful.

I can't find the link to them at the moment, but will let you all know when I find it. We made a batch of little "filler" rigs for a customer a little while ago. Boxed and ready-to-run, they cost about £80 each to build.

[RF-Head]

@ Albert,
You tell us many times that you make lot of transmitters
But you never show any picture
I realy like to see what you make

[Albert H]

Perhaps you should pay more attention to the forum. I posted a few photos of some of our gear a while ago.

Most of the stuff we make is in 19" rack boxes. Aluminium and steel boxes with a few sockets on them are not very exciting! The boards inside are proprietary, and I really wouldn't want to give anyone the opportunity of copying our layouts. Some of them have been developed over many years, and we use a few unique tricks to minimise conducted RF on power cables, to reduce noise, and to enhance signal purity and stability. We always use either crystal ovens or off-air circuits for frequency references. Any crystals on boards without ovens are not frequency critical (for example clock crystals for microprocessors, AVR or PIC devices).

We also have unusual approaches to thermal management - not necessarily unique, but we're quite proud of them.

You will probably have seen some of our MW boxes if you've visited some of the little AM stations in the Netherlands. They're just anonymous 1U 19" rack boxes with XLR audio input, N-type RF out, and IEC mains input. They have controls behind a screwed-down flap on the front panel - rotary frequency-setting switches and modulation setting controls. We include comprehensive audio processing in the box, with a three-band compressor / limiter, so that it provides a one-box solution for small AM stations. These have also become quite popular in Africa and South America for local broadcasting. We also provide a shortened vertical dipole (two helically wound elements) for the top end of the Medium Waveband, which has a surprisingly good radiation characteristic for a short aerial!

On a forum like this I really wouldn't want to run a commercial advert. You may well have seen our advertisements in the Broadcast trade magazines.

[jvok]

How tall was your shortened MW dipole Albert?

Also why a dipole instead of a 1/4 wave vertical? Just so you don't need the ground system?

[RF-Head]

Albert,
I visit most of the LPAM stations over here in NL but not seen any of your AM transmitters in 19"case
Most of the stations using home made transmitters or PLL.GR or from Arjan Bussum
What stations is using it then ?

[Albert H]

How tall was your shortened MW dipole Albert?

Also why a dipole instead of a 1/4 wave vertical? Just so you don't need the ground system?

It's about 11m tall. The counterpoise element is to get rid of the need to work against a ground mat. Radiation efficiency is pretty good as far as shortened aerials go.

The idea came from an article in the late 80s in Radcom for a Top Band (160m) helical dipole. The prototypes were wound from about a quarter wavelength of wire for each element with a tapered wind along a fibreglass "roach pole" fishing rod. The feed point impedance is of the order of 8Ω, so a matching network is necessary to transform to match 50Ω. We used a balun which was quite broadly tuned. The other issue we expected was usual the narrowed bandwidth of shortened aerials, but we found that the bandwidth was more than we expected, and we didn't need to take any measures to handle that.

The only problems we encountered were supporting the feedline away from the elements, and finding something to hang the aerial from! It's not practical below about 1 MHz because it gets rather big, but if you want to use it at the top end of the band it works rather well.

We've used these for "RSL" installations and at festivals. There are also a few in full-time use in South America.

[Albert H]

Albert,
I visit most of the LPAM stations over here in NL but not seen any of your AM transmitters in 19"case
Most of the stations using home made transmitters or PLL.GR or from Arjan Bussum
What stations is using it then ?

We've sold about half-a-dozen in NL. We've not ever seen you at our LPAMs. I'm not going to tell you the brand on a public forum (voor duidelijke redenen).

Are you in Haarlem?

[rigmo]

Weirdly, I saw a Chinese "20 Watt" amplifier board that was nicely laid out, included a FET that would actually achieve the rated power (and a bit more), had a reasonably good output filter, and only needed about 300mW of drive. It had to be run at 18V to get the 20 Watts, but it worked OK and was clean. These came from a factory in Kowloon (where Uniden used to get boards made), and cost around £20 each, or less if you bought a boxful.

I can't find the link to them at the moment, but will let you all know when I find it. We made a batch of little "filler" rigs for a customer a little while ago. Boxed and ready-to-run, they cost about £80 each to build.

we wait this information

[sinus trouble]

Albert does not need to post anything that he doesnt want to!!

Infact there are many pics of past rigs that i would love to post! Unfortunately Digital media was non existent in those days, Pics that i did take have been lost!!

Anyways back to subject! I was thinking of designing a universal version of these very PCBs! There are some decent TO-220 packages available which could be easily be implemented for a desired application!

[reverend]

I was thinking of designing a universal version of these very PCBs! There are some decent TO-220 packages available which could be easily be implemented for a desired application!

That's where I was headed - to see if there was a PCB design that could be borrowed/adapted/made to work with different transistors. Sadly, this one is not it!