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Title: using electric guitar amps as a modulator Post by: KK4RF on August 16, 2009, 09:48:37 AM Has anybody here ever tried to use an electric guitar amplifier as a modulator for an old cw transmitter? I have 5 sons who've collected a bunch of guitar amps, tubes as well as solid state, in the 30-50 watt output range and wondered about using a tube audio output transformer backwards with some filter chokes in a Heising type modulator circuit. I wondered if anybody here had tried that.
I'm new to this forum. Any opinions on this would be appreciated. Thanks. ---Marty, KK4RF--- Title: Re: using electric guitar amps as a modulator Post by: W3SLK on August 16, 2009, 12:01:23 PM Marty said:
Quote Has anybody here ever tried to use an electric guitar amplifier as a modulator for an old cw transmitter? I have 5 sons who've collected a bunch of guitar amps, tubes as well as solid state, in the 30-50 watt output range and wondered about using a tube audio output transformer backwards with some filter chokes in a Heising type modulator circuit. I wondered if anybody here had tried that. No they won't work! You need to send them all to me immediately! ;) Seriously, with some slight modifications, you can make them work as a dandy speech amp. I use a Bogen PA amp to drive my 805's on my HB modulator. Find a UTC multi match xformer and you will have something along the lines as an Eico 730. Title: Re: using electric guitar amps as a modulator Post by: kd4afp on August 16, 2009, 12:21:07 PM Hi Marty;
Here's a link to a tutorial by Stephen Ickes, WB3HUZ that shows how to do what you describe: http://www.amwindow.org/tech/htm/obmod.htm 73, Rick KD4AFP Title: Re: using electric guitar amps as a modulator Post by: w1vtp on August 16, 2009, 12:48:05 PM Marty
Here's what I did. Look for the PDF file and take a look at it. Yes, you can use an audio xfmr backwards. Just be careful about the amplifier you use. I had a so called 50 watt amp and the iron in it was pathetic. Remember, garbage in, garbage out. http://amfone.net/Amforum/index.php?topic=16771.msg115834#msg115834 73 es GL Al W1VTP Title: Re: using electric guitar amps as a modulator Post by: KK4RF on August 16, 2009, 02:51:05 PM Gentlemen,
Thanks for all the replies to my question on guitar amps as modulators. We've got 3 tube amps here rated at 30 watts out and 1 solid state unit rated at 50 watts. For the most part, they sit idle here and I've been wondering they could be pressed into service as a modulator. I'd seen the nice article about using Hi-Fi amps as modulators which is what got me to thinking about all these guitar amps around the house here. I've been getting on 3885 kHz with a couple different rice-boxes and have been amazed that people actually can hear me on AM with just 25 watts out. I do have an old WRL Globe Scout which I'm buying some crystals for and hope to have up on 3885 in the next couple weeks. I suspect my output from that old tube . rig would be close to my rice-box units. It would be fun to get on AM with an old tube rig! Thanks again to all for answering . 73s, Marty, KK4RF Title: Re: using electric guitar amps as a modulator Post by: N4LTA on August 16, 2009, 05:26:36 PM One thing to keep in mind when using a Push Pull output transformer in reverse. A push pull output transformer is not designed to pass DC current and may quickly saturate when used as a modulation transformer. In a push pull output transfomer - the currents in the core cancel each other. That will not be the case when using it in reverse as a modulation transformer.
I have used one of the heavy Hammond SE series of transformer as a modulation transformer with a solid state amp driving it. The large ones are rated for over 100 MA current. Title: Re: using electric guitar amps as a modulator Post by: WBear2GCR on August 17, 2009, 10:13:22 AM actually the thing you need to be most cautious about is the setting of the gain and tone controls, since most guitar amps are designed to distort quite a bit. I'd put it on a scope and look for the best settings - use a square wave at 1khz. and adjust for the best looking flat top you can get, then use a triangle wave at the same tone settings and look at the input level vs. output level for the best gain control settings... _-_-bear |