Checking Modulation On An AM transmitter Using Two Different Speech Amplifier Drivers. 

No audio bandpass filter in my AM transmitter. In SSB transmitters, audio bandwidth is generally and intentionally limited to about 3 KHz (the voice range of 300 Hz to 3 KHz) and only one sideband (thus, single side band). In AM there are two sidebands, the plus and minus audio frequency of the modulated carrier frequency so, AM is, at the least, twice as wide as SSB. In addition, we really don't get into trying to narrow our voice sideband (either one...) to some, really nice level, meaning we go ... HiFI... Not everyone loves us but we don't care. Kind of like playing your stereo a little loud in an apartment complex. With that said, I got a comment recently where some fellow, that was very strong at my location, told me I was 15 KHz wide - that would be a 7.5 KHz audio signal. With his signal level at my location at S9+, no doubt he was correct as he would have also exceeded his 3 KHz (nice neighbor level...) boundary. It prompted me to measure my bandwidth, especially concerning the "fidelity" i.e. "bandwidth" of my modulated signal. I am satisfied that sounding good is not a violation of respectful ham radio etiquette and this is my documentation of different levels of "fidelity" in AM transmissions. From the other side of the isle, the SSB community, many try to sound HiFi with their high-end microphones which invariably adds bass frequencies to their audio, in a SSB restricted frequency range, and it only ends up making them sound "bassy" and hard to understand with the least bit of QRM (interference) . In the SSB communication world, a person should actually try to sound like the space shuttle talking to Houston and not attempt to sound like a high fidelity amplitude modulated transmission - which the SSB mentality is likely to criticize the AM community for sounding like -

Wow... three 3-500Z's. That should deliver the legal limit and some. I haven't built anything significant in a while and don't have plans for anything at the moment. I still think about building a 833A class-C RF amplifier and plate modulating it with maybe a pair of 4-400A. That could happen as I have all the big parts but I need more room. 73

Thank you for your kind comments. I used to budget myself to about $40 to build an amplifier - that was around 50 years ago. Nowadays with Ebay, things like transformers are much more accessibly than they were 50 years ago (back then we had to part-out old TV's or have a buddy with parts) but the prices are astronomical nowadays. Buying every part new, except used output transformers off Ebay, could easily cost $800 or more to build a 20WPC tube power amplifier. The only reason I can still do some of this is I have a 60+ year supply of parts. I started as a ham radio operator at 13 and been hording every since. 🙂 With all this said, the 1947 design known as the Williamson design is probably the best 15-20 watt power amplifier ever produced. There are lots of schematics for Williamson designs but my favorite is the 6SN7 version of the Heathkit amplifier. Here is a site with all the Heathkit products and the amplifier version is the W-5M that I like - way down at the bottom of the list of products. Hope this helps you build. www.vintage-radio.info/heathkit/

20 dBm is 100 mW (0.1 watts) so make sure you do not exceed that level or you will fry the input. If it is 50 ohms that is a maximum of 2.24 volts. Check my math to make sure I am correct. I always keep at least a 20 dB attenuator on my HP SA and a DC block. Some SA's require Zero DC on the input. I just looked up your SA and it is 9KHz to 2.1 GHz. I hate to tell you this but it won't work very well at audio frequencies if that is what you want to use it for. The PC based SA's are the best for audio work. Hope this helps.

@ElPasoTubeAmps OK thanks I will return this unit do you recommend a PC based unit SA.

@@nigman2023 I haven't used mine in a while but the one I find on my PC is TrueRTA. As I remember, the SA was good but the oscilloscope was not good. There is another one called SpectraPLUS but it is really expensive but you can use it free for 30 days. www.trueaudio.com/rta_down.htm www.spectraplus.com/Downloads.htm

Mine is the, SDRplay RSP 1A. I see them on Amazon for about $179 or they can be bought many other places maybe cheaper. Ham Radio Outlet and many other ham radio sellers have them. www.hamradio.com/

I am in El Paso but I can't take in amplifiers or other equipment anymore. Just too heavy and I can't make the commitment. In addition, I am only set up for vacuum tube equipment. Just for curiosity, what high power level are you talking about? I know there are some KW level solid state amplifiers out there. A few years ago one was brought to me and it was absolutely burned to a crisp. Someone must have shorted out the fuse/circuit breaker and it literally caught the PCA on fire. Thanks for asking.

@@ElPasoTubeAmps Daing. Sorry to hear that. Its not monstrous. Its just very special and a classic. All the big area rockers used them from what ive read. Metallica and such. It was used by a family friend till he passed. Its one of the biggest and most expensive MESA BOOGIE amps they ever made. From what ive gathered. Ive had it 22 years. 300 watt "COLISEUM Series" guitar amp. VACUUM TUBE. I really didn't want to ship it to California. Back to MESA. COLISEUM 300, MARK-2B. Im pretty sure. Discontinued

Building an 813 linear amplifier has interested me for years as I have several 813 tubes. You may have just renewed my interest. I hear they make a good SSB GG linear amplifier. There are lots of articles on 813 amplifiers on the Internet and here is a link to one. www.w4npn.net/813-linear-amplifier-project/ Building multiband amplifiers is a serious addition over a single band amplifier. The easy way to solve that is use the B&W 850A tank coil that sometimes come up on Ebay although many are in terrible shape. Many people chose not to tune the input as a pair of parallel 813's have in input Z of about 100 ohms and most modern day auto-tuning rigs can handle that but I think tuned inputs are a good idea both in harmonic suppression and ease of driving the amplifier. For single band RF amplifiers, 1/4 inch copper tubing or #8 solid wire make a good tank coil and is what I have used for years with 4-400A amplifiers. Maybe you want to build your own amplifier. 73 WA4QGA

​@@ElPasoTubeAmps Thank you very much for your response. Thats exactly what Ive been kicking around for a while, iam confused with what transformer to use, I was told an intermiadiate duty transformer @2,700v but Iam confused with what happens when iam finished rectifying and filtering the secondary, the voltage seems a bit high for the 813's liking.