• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Guitar Amp, Phono Amp, Blue Tooth AM Radio

Hey Gang,

Recently, I was thinking about adding the aforementioned things in the title to am old AM radio. I recapped the line caps (AA5 Radio) and removed the hum, and I'll eventually recap old caps that need replacement for proper bias and so forth, accordingly. (Will run em through ESR and so on.)

Looking around on YouTube, I've noticed A LOT of videos that say to just jump on in on the volume control -- fine with low-voltage DC, but not with high-voltage-DC circuits we get with tubes --and a lot of folks out there are doing so and NOT taking the high voltage on the grid input seriously and as an electrical-shock hazard! That is, a lot of these videos -- most, if not all, mind you -- are going straight-line to the grid.

Some do use coupling caps to feed the audio, but as most of us are aware, if that cap shorts closed, they'll have 250-300 VDC right on the input jack(s). The seriously sad thing here is that I'm seeing this garbage on factory-built, guitar amplifiers. Other than that cap, there is no physical isolation being used.

I was told in another forum that I could use an old 600-600 transformer out of an old transistor AM radio to solve the issue, but I'm not really sure of the exact setup to do such a thing. I would guess that I could take two stereo leads from the line-level output of my computer and connect each lead to each input lead on the primary, ground one side of the secondary, and head the other lead over to the volume control? I guess I could even add a variable RC network for a bit of tone control at that point as well.

I got to thinking about all of this a bit more, and I'm wondering if the 600-600 transformer is going to be the correct input impedance for the tube, and my brain tells me, "No! This has to be calculated for the correct impedance for maximum-power transfer!" :D. OTOH, would this be overkill? Can I get away with just using the AM-radio transformer? If not, I have a TON of Amidon cores hanging around, so winding my own transformer shouldn't be that big of a deal, I'm guessing. I know Amidon has some info out there on how to best use their cores, so I'm sure that could help.

I guess I can do some switching on the input jacks, which would allow 3.5mm, RCA phono, and 1/4" inputs to be selected as well, and I should be able to purchase a stereo Bluetooth receiver on the cheap on Amazon or E-Bay. Any suggestions?

BTW, I'm a software engineer, and I am self-taught in electronics, but I think I might get the gist of the situation if you could explain where I could be going wrong, or a helpful point in the right direction might work just as well.

73 [Best Regards in morse code :D],

Randy AB5NI
 
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> AA5 Radio
An AA5 radio used for ANY non-radio purpose MUST have a power isolation transformer.

There's multiple misunderstandings in your post but let's first keep you alive.

Well, I have a Sencore AC "Powermite" sitting here on the bench. Hope that will work :D. I also have a dim-bulb setup as well.

73,

Randy AB5NI
 
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> Sencore AC "Powermite" ...Hope that will work

No.

You do realize that the Sencore Powerite is an isolation transformer, with an included variac and safety analyzer, right? Search for it with your favorite search engine. I have also plugged in numerous AA5 radios into a dim-bulb that is plugged into the Sencore and slowly bring up the voltage on a new radio to fix to reform the caps.

So, now that we have the safety stuff out of the way....

[EDIT] My bad. I said it was powermite, but it's actually powerite. It's few feet out of my reading-glasses range :D.


73,

Randy AB5NI
 
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Well, let me see if I can make this easier. Will this work for a 3.5mm stereo input?

AA5-JACK-INPUT.png
 
Oh, wait. My bad. You are talking about a transformer for the AC line. Well, I didn't plan on adding one. I know you guys are all "safety first" here in the forums - I actually read the do's and don'ts before posting.

OTOH, I have been playing around with very-high voltage for many years, building numerous 3KV 3-500z and 3 and 4-1000 amplifiers for RF work. I am very aware of the danger, first and foremost, and I always take it very, very seriously. "Left hand in back pocket," shorting the caps through a bleeder, and so on, PRR. I have been playing around with high voltage for almost 50 years, for the record. Tubes and valves are my friends :D. I really do appreciate the concern, as you don't know where I'm coming from.

73,

Randy AB5NI
 
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Someone with an Extra class license should understand that....

The chassis ground that you draw in your transformer schematic is connected DIRECTLY to one side of the AC line. Many radios do not have a polarized line cord, and those that do may or may not be wired correctly. So connecting something like a guitar into one of these radios can be exactly the same as plugging that guitar into the line socket.....you have a 50:50 chance that your guitar cable is connected to the HOT (black wire) in that outlet.

Now consider how you hold a guitar. The hand you wrap around the neck will go into an involuntary contraction making it impossible to let go if another part of your body finds its way to a ground connection.....you can be FRIED!!!! People have been killed by gripping a hot guitar in one hand and grabbing a grounded mic with the other.

The FIRST step to playing with these is to get a small isolation transformer like a Triad N-68X and wiring it between the radio and it's line cord. It's a $15 insurance policy that could save your life....and it will eliminate ground loops and the associated hum issues.

Be safe...... KB4LRE
 
Howdy Tubelab,

Hey, I get where you guys are coming from, Tubelab, and I understand it completely. I've already changed the across-the-line cap with a proper safety cap, btw. Actually, that's the very first thing I do when working on a AA5. I've also installed a proper cord as well, which is polarized correctly, but there is a problem... :D

Another issue I have is that this house was built in the 60's and wired with 12-2 with no ground, making things even worse, so what I'm left with is neutral and hot. Man, PRR is really gonna be disgusted with me when he reads that! A apologize beforehand, PRR! :D

Unfortunately, I no longer have the health to run proper wiring across my home to my ham shack. Even if I could do the work myself, there are clauses in insurance contracts that state something along these lines: "If you wire it yourself and it causes your home to burn down, we ain't paying you crap!" So, what that means is that I have to hire a certified electrician to do the work and have it inspected, and that's not cheap. Kind of a hard thing to do when you're living on a fixed income. (I'm paying for my Mom's in-home healthcare, which is leaving me kinda strapped for cash.)

Wait. I think I might have a saving grace. About 20 years ago or so, I had an electrician install a 220 line for my amplifier(s). It was a new run, so I take it that he wired the thing properly for code. Why couldn't I just rewire that run for 110? Would that suffice and make you guys happy?

As far as using an AA5 for audio amplification goes, I was thinking along the lines of this: It would be a cheap way of hearing semi-decent, single-ended class A audio amplification. Adding a power transformer would remove the overall visual aesthetics, because now it's going to have an external supply attached to the thing. Yeah, I can hide it and whatnot -- I get it, guys.

Another consideration: If I have to build a supply for safety, I might as well just rebuild the whole damn thing properly, and if that's the situation, I might as well do it right and build a proper mono-block amp, based on a 12AX7 and a 6V6 or something. I'm sure there are some amps you guys would highly recommend here on this site, but there is a problem...

Now I've gone from a simple AA5 setup to spending a lot of money on a mono-block amp, and if I want to have stereo, I'll have to build another. Do we all see where this is heading? Let's just call it $$$ for good measure :D. I guess I could build an integrated amp, but, personally, I'm not much of an integrated fan.

What my long-term plan to do was jack into the AA5, add Bluetooth, WiFi (to control the input switching via my cell phone or web browser), and use the amp to hear some semi-decent tube audio from whatever I had connected. This project has now gone from $20-$30.00 to possibly $500.00 or more. Maybe you guys could tell me how to do this on the cheap. (Shrug.) BTW, I will be using the Powerite until I decide on what to do. Suggestions really appreciated!

73,

Randy AB5NI
 
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The AA5 radio uses series filaments to allow 5 tubes to work directly from 115VAC.

Not an issue.

The AA5 DOES NOT have a transformer. It is direct line driven and one side of the AC line is connected to chassis. With a non-polarized AC plug you have a 50/50 chance of connecting AC Line to chassis making it a "Hot Chassis" device. If you touch the chassis and are standing on a conducting surface (cement) without sufficient insulation, you are subject to electrical shock.

An Isolation Transformer is necessary to make the AA5 electrically safe.

(Why did not lots of people get electrocuted? They were housed in either wood or plastic housings.)
 
I am very, very, very, well aware that AA5 radios have no transformers and use voltage-doubling circuits to achieve B+ voltages. I know -- without any doubt whatsoever -- what I'm dealing with here. Although I am self-taught, that doesn't mean I don't know what I'm doing. I have studied electronics engineering and computer engineering for what -- 40 years or so now. I still get some things wrong, time and again, and I've never done this before, which is why I'm here looking for suggestions.

Yes, I can get on E-Bay and order a filament and power transformer, bridge rectifier diodes, filter caps, and whatnot to build a brick-craphouse supply. I get this, without any doubts whatsoever -- come hell or high water. I completely and utterly understand the perils when dealing with AA5's being connected directly to the mains.

Do I understand audio as well as you folks -- not even close! I was hoping to come here and converse with kindred spirits, and all it seems to be coming down to is that I'm getting flak about trying to do this cheaply with an AA5. I understand that you don't like this, no problem.

I have been trying to be humble here and introduce myself in a very humble manor. Being raised by educators, I've learned that everyone loves to teach, and I'm TRYING to give you that latitude, whether I already know the subject matter or not. I am WELL aware of the dangers -- and then some.

I really, really appreciate where you guys are coming from, as you don't know me or my capabilities. I understand. Thank you for watching out for me! That being said, I was hoping that this topic could somewhat glue me to the group and allow me to introduce myself in a humble manor -- evidently not.

For the record, and just in case you think I'm over-reacting, this is my personality type:
Introduction | Advocate Personality (INFJ-A / INFJ-T)

| 16Personalities
. Most people get this wrong about me, so I understand.
 
I don't know if you are being difficult on purpose, or just overreacting to criticism, which was intended to be constructive.

You don't need to build a completely new power supply, or rewire your house, or specially wire it to your 240V service, or spend a lot of money. You need to add an isolation transformer, like the $15 item recommended to you.

I honestly wonder if you are trolling, since why do you own a fancy (for my budget) item like the Powerite, but are arguing that you don't need isolation?
 
Another issue I have is that this house was built in the 60's and wired with 12-2 with no ground, making things even worse, so what I'm left with is neutral and hot.
One thing that really bothers me, one is not allowed to buy 2 prong outlets with one big (neutral) and one small prong. In fact no local store has 2 prong outlets at all. Lots of appliance now come with that sort of plug, it avoids the problem of the appliance being plugged in "upside down". Your re-equipped radio has that sort of plug, you said.
It is totally un-code to put a 3 prong plug on a 2 wire romex supply. So the US standard way to solve the problem is to pay an electrician (making $25 an hour minimum) to have all the walls of the house bashed out, replace all the wiring, then replace all the walls with new wallboard. Bleah. $$$$$. Paid an electrician to do it to the wife's computer room, and he talked her into putting a line surge arrestor in the meter box and pocketing the money anyway. !!!!!!
BTW rented a house when I first moved to this town where all the white wires were hot and all the black wires were neutral. Plugs were backwards too. Found out trying to fix a hot chassis TV. Was offered the house for $11000, didn't take her up on it, moved away to a $40000 place that has 3 prong outlets & 3 wire romex in most rooms. But not the outlet where my sound system is plugged in, that one has 3 prongs and 2 wire romex. !
BTW if I was playing guitar into a tube amp, I'd want 1000 v capacitor between me & grid, or if a 600-600 transformer as you propose, one that had been subjected to a hipot test. IE 1400 vac primary, how much leakage comes out of secondary. Audio transformers may not be wound with 600 v insulated wire, and US house current has 1300 v spikes on it from the AC or refrigerator compressor shutting off. Vacuum tubes are great for making a certain guitar sound, TL072 op amps are great for guitar pickups that don't expose the musician to lethal voltage on bad days.
Makes me happy I play organ with plastic keys between me & the high voltage. Don't touch the drawbars, only the handles!
 
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I don't know if you are being difficult on purpose, or just overreacting to criticism, which was intended to be constructive.

Well, if you read my link to my personality, I'm probably overreacting, as usual :D. OTOH, the vast majority of the responses I've gotten have all been about the dangers of AA5 radios, which I'm well aware. I tried to hint at this in a humble manor, multiple times, yet the responses I'm getting are still about the dangers of AA5 radios. For the record, I ordered 5 of those transformers.

You don't need to build a completely new power supply, or rewire your house, or specially wire it to your 240V service, or spend a lot of money. You need to add an isolation transformer, like the $15 item recommended to you.

As mentioned above, already done. I guess I should have said that I already ordered them earlier.

I honestly wonder if you are trolling, since why do you own a fancy (for my budget) item like the Powerite, but are arguing that you don't need isolation?

The plastic, RCA Victor AA5 is plugged into the Powerite, of course. So, when you think about it, I do have isolation. I was not aware that I could get an isolation transformer that cheaply, which is one of good reasons for visiting a forum such as this, of course.

As far as trolling is concerned, that is something that I've never, ever done in my life, and that's since I've been on the BITNET in the 70's. Also, I was fortunate enough to get the Powerite for free from a friend that shut down an old TV repair shop. He also gave me a CRT analyzer and some other test gear. I asked him if he had a spectrum analyzer hanging around, and he said "Nope, but you couldn't have that anyway!" LOL!

As far as the other stuff goes, I guess I was just rambling on about things that should really be done around here. A nice, variable supply with good voltage and current-handling capability would be nice, and the wiring does need to be changed. I think everyone would be in agreement on that. (Shrug.)

73,

Randy AB5NI

P.S. I have an extremely rare personality type, and everyone usually pegs me wrong -- and then some! -- which is why I try to use a lot of LOL and smilies in my posts and responses. Over the years, I've learned that there is no body language and things can often be taken in the wrong context. I love life and embrace my friends and family wholeheartedly, and I'm trying to project that to my friends on the net. Have I succeeded. Nope! EPIC FAIL! However, that doesn't keep me from trying! I guess u can just color me weird or something :D.
 
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One thing that really bothers me, one is not allowed to buy 2 prong outlets with one big (neutral) and one small prong. In fact no local store has 2 prong outlets at all.

Yeah. There a shoot-back to the 60's, and they have no reason to carry them anymore. You might be able to pick some up at a swap-meet or ham fest for 50 cents. Be on the lookout. I guess you could make your own with a 3D printer? That might be worth a shot.

Lots of appliance now come with that sort of plug, it avoids the problem of the appliance being plugged in "upside down". Your re-equipped radio has that sort of plug, you said.

Well, what I did was use an old computer power cord, and I left the ground lead hanging and shrink-wrapped. You can pick them up for $1.00 at a ham fest. I have around 20-30 of em in the junk box. It is also important to note here that, although my wiring doesn't have ground, I have replaced most of the sockets with the three-pronged version. Got tired of looking for adapters
:D.

It is totally un-code to put a 3 prong plug on a 2 wire romex supply. So the US standard way to solve the problem is to pay an electrician (making $25 an hour minimum) to have all the walls of the house bashed out, replace all the wiring, then replace all the walls with new wallboard. Bleah. $$$$$.

Tell me about it, dude! I was wondering if I could tie up some new romex to the old cable and pull it through, but then I got to thinking about it decided it was not going to work :D. What I think you might be able to do is get a razor knife and find out at what level the romex is being run, and after that only cut a, say, 3-4" slice out of the wall, from that point on, and then make the the cable run.

I have also seen setups where they just make drops from the attic down through the wall, and then they just use a small circle cutter and fish it through. Once they have the cable, they just cut it up square to match the junction box. Maybe that might work in your situation?

Paid an electrician to do it to the wife's computer room, and he talked her into putting a line surge arrestor in the meter box and pocketing the money anyway. !!!!!!

Do what?! I remember back in the 80's when those were popular. Some companies were even putting some line-conditioning device just past the meter, saying they were "protecting the house" and lowering the overall electric bill :D. Hey, they might actually work at protecting stuff, but I'm kinda sketchy on lowering the bill past the meter :D. Hey, maybe so, but I kinda doubt it, dude :D.

BTW rented a house when I first moved to this town where all the white wires were hot and all the black wires were neutral. Plugs were backwards too. Found out trying to fix a hot chassis TV.

Wow. Sounds like a journeyman who was just starting out wired the place. LOL! BTW, you might want to check out "Shango066" on YouTube, if you're into fixing old TV sets and radios. He's very funny and very entertaining. I really enjoy his videos when he's fixing the old console setups from the 50's and 60's. I'd love to get my paws on some of those high-efficiency speakers from back in the day. 4-5 watts and blast out the neighbors :D.

What I'd really love to do is get a couple of exact-match consoles, rip out the amps and the high-efficiency speakers, and then use something like a Technics 1200 turntable and see how that sounds in my listening room.
Not sure which console I should search for, though. Maybe somebody could make a suggestion. Locally, a few years back, I've seen them going for $15.00 and such -- just my budget :D. I'm thinking that something like a 6BQ5 final would fit the bill nicely. All single-ended, class-A amplification, of course. :D

Was offered the house for $11000, didn't take her up on it, moved away to a $40000 place that has 3 prong outlets & 3 wire romex in most rooms. But not the outlet where my sound system is plugged in, that one has 3 prongs and 2 wire romex. !

Man, that 11K home prolly goes for something like $100K, these days. Hindsight is a wonderful thing, though. LOL!

BTW if I was playing guitar into a tube amp, I'd want 1000 v capacitor between me & grid, or if a 600-600 transformer as you propose, one that had been subjected to a hipot test. IE 1400 vac primary, how much leakage comes out of secondary.

I was actually thinking about adding both, just to be on the safe side. Who knows? In 20 years my niece might inherit the thing, and the ESR leakage might fry somebody. This is why I like to put a "Last Repaired Date" piece of tape inside the gear. Should a tech come across the thing, they'll know that years have passed and be wary. I know I would. (Shrug.)

Audio transformers may not be wound with 600 v insulated wire, and US house current has 1300 v spikes on it from the AC or refrigerator compressor shutting off. Vacuum tubes are great for making a certain guitar sound, TL072 op amps are great for guitar pickups that don't expose the musician to lethal voltage on bad days.

You bring up a good point. There is no possible way in hell those 600-to-600 audio transformers out of AM pocket radios would be wired for that. The factory would never, ever spend that kind of money, which means I'm going to have to locate one rated at high voltage. Guess I'll have to search and see what I can find.

TL072's, huh? That's a blast from the past :D. Can you actually still find those about at a reasonable price? Guess I'll have to search for that as well.

Makes me happy I play organ with plastic keys between me & the high voltage. Don't touch the drawbars, only the handles!

I hear ya, dude. My Dad taught music, and he had a 6.5 foot Steinway in the living room that I used to play a lot. Came back home from Houston -- was designing and maintaining Jack-up and Semi-submersible simulators for the oil patch -- and my Sister "lifted" the piano to teach her daughter. I was kinda ticked off :D, but I wound up with a Kurzweil 250 to hack around on. I always wanted to see if I could get my paws on a Hammond for cheap. I wonder if they're still around and available at reasonable prices? Yet another search :D.

73,

Randy AB5NI
 
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Found an A100, which is a B3 with a whole case and it's own 6AQ5 pushpull power amp, for $75 at Salvation Army resale. Was missing some front veneer and the power tubes were gone. Came under their "distressed" pricing policy.
You see those sometimes on TV with bands, though not the top end ones.
Hammond H100 are still $100 nearly everywhere, although they require some preamp rewiring to have 3's percussion like a B3. You also have to turn off the extra 3 overtones. I use those overtones when I'm trying to play "Telstar", makes a shrill screech like that mellotron or whatever that was.
 
I always wanted to see if I could get my paws on a Hammond for cheap. I wonder if they're still around and available at reasonable prices?

I found this M3 at a Goodwill store for $39.95. I was told that due to it's age it was not tested and the plug was cut off to prevent anyone from plugging it in. It was being sold as "furniture." Upon getting it home I discovered that the cord was still intact, just stuffed up inside, so you know what I did......It works perfectly too. Made in 1957 it still has all it's original tubes and capacitors.

The M3 is known as the "baby B3" but it isn't exactly a lightweight at 250 pounds. It's what Booker T (Green Onions and many more) learned his chops on.

I remember seeing an M3 offered for cheap somewhere in this forum. Try searching here!

play "Telstar", makes a shrill screech like that mellotron or whatever that was.

The original recording of Telstar by the Tornadoes dates to 1962, before the Mellotron was developed. There is some speculation as to exactly what made the screechy sound. Some say that it was a Clavioline, some say a Farfisa, and others say it was a cheap plastic organ mic'ed up.

The Ventures did a cover of that song in 1964 using a Vox Continental organ.

The Mellotron was actually the first "sampling keyboard" using a strip of magnetic tape for each key. It could sound like whatever was recorded on the tapes.
 

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Found an A100, which is a B3 with a whole case and it's own 6AQ5 pushpull power amp, for $75 at Salvation Army resale. Was missing some front veneer and the power tubes were gone. Came under their "distressed" pricing policy.

Damn. Nice find, dude. I really miss the days when you could walk into Good Will and The Salvation Army and find stuff like that for pennies on the dollar.
Pawn shops were wondrous, back in the day as well, as far as guitars were concerned. If you needed a bit of extra cash or just wanted to find something for your collection, you just popped on over, nabbed it for $20-$50.00, repaired it, and either listed it on E-Bay for a nice profit or added it to the collection. Unfortunately, the net woke everyone up on prices, so doing something like that is near impossible these days.

You see those sometimes on TV with bands, though not the top end ones.
Hammond H100 are still $100 nearly everywhere, although they require some preamp rewiring to have 3's percussion like a B3. You also have to turn off the extra 3 overtones. I use those overtones when I'm trying to play "Telstar", makes a shrill screech like that mellotron or whatever that was.

I don't know jack crap about Hammond organs, although I wouldn't mind finding one on the cheap and repairing one to play around with, for sure. All I really want to do is learn how to play like Billy Preston in this video:
YouTube

To me, THAT is a Hammond player! He totally gets it that great music is a heartfelt, soulful, emotional experience, which is a rarity in the music world. I guess that's why we all enjoy it so much when a great musician can play and project like that, for sure. About 3 minutes into the video is when he really gets after it.

If I remember correctly -- bad diabetic, so my memory is shot -- the keyboard player for The Moody Blues used a Mellotron? I think I remember hearing him talk about it in an interview or something. I'm trying to imagine being a tech for the band and having to repair that thing on the road. I'm not sure you could pay me enough for that, so I probably would have concentrated on sound engineering and mixing. LOL!

73,

Randy AB5NI
 
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