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Discussion in 'Shock Brother's DIY Amps' started by Prophetsnake, Sep 27, 2019.
I believe it’s the deep.
If you have a output transformer you have the most expensive part needed. A power transformer is next on the list but there is a low buck way around that but I'll leave that to later. Years ago I took part in a diyAudio $100 Guitar Amp Challenge, over 100 pages of Silliness. I think about four legitimate designs came out of it but being North America based shipping would be a problem. I was the only one with a complete parts list, knobs included, bend your own chassis, most everything from Antique Electronic Supply. It resulted in a 12AQ5 cathode biased 6G2 Princeton with no vibrato. If I were to make a Tweed style amp of that wattage I would use that design.
I have done a few of that circuit, I used a 12AX7 and a 12AV6 for the three triodes. I used a 12V transformer to feed the heaters, the 6V6's could be put in series or you could use 12V6's if they are available, or if you want to be different, 6AQ5's or 12AQ5's. These alternate tubes can be had relatively cheap if you are lucky, might as well get enough replacements while you are at it. I did manage to drop a triode by using a MOSFET in the phase inverter position, saves a tube and socket, a little on heater draw also.
The IRF820 has been used a lot in place of a cathode follower in the amp building community, there is a variant, IRF830 with an insulated tab. Zener can be 5-12V. If a couple of more parts can be managed the above tone stack gives a bass and treble control an a less midrange sound, the switch adds the midrange back and the treble functions somewhat like the Tweed circuit. The phase inverter 47k resistors can be anything from that value up to 100k. But then again the simplicity of the tweed tone control is hard to beat.
Now as far as power transformers go, I have tons of them from parting out old electronic equipment. But as alternatives I have used the 186D120 http://www.hammondmfg.com/186_187.htm which is a 30VA transformer and used 12V transformers for the heaters. There sould be some 1:1 30VA transformer's availible for your voltage and rectifying it should get you in the range. Lately I have been using 12V laptop or wallwart dc supplies for the heaters. And moving along on the switching power supplies I am going light weight with laptop supplies for the heater and a China high voltage switching module fed by the laptop supply. As you can see, no rectifier tube in any, silicon diodea are fine, if you want more sag put a resistor in series with the PS.
Just some ideas.
That's nice! Is that challenge somewhere in this forum?
Yeah, one of my first attempts was with a Boot Hill 5E3, and you're right - no iron. It is a very good kit though, and Boot Hill was the perfect choice for the level of skill I had then.
I mentioned above that I've selected an old Danelectro circuit as a project for this guy. The parts count is low, it's simple enough so even I can understand what's going on and the demos I've seen blow me away. I had some parts already, so the small stuff I needed was only about $40. I have what I hope is a suitable OT, but the PT I have might be a bit small for the task. I'll try it and see what the plate voltage gets up to and if it wimps out on my, I'll cross that bridge when I come to it.
This is the planned amp.
That's nice! Is the $100 challenge somewhere in this forum?
Link please? That looks great.
What do you mean “no iron”?
Don't forget Facebook marketplace. I just got an old record player on there for $9 that has a working amp with 2 6v6's, an RCA 12AX7 black plate and a 12AT7, 6X3 rectifier tube, output transformer, and comes in an awesome wooden box. People are just giving these things away.
Here is the link to the Instrument forum, the $100 Challenge is a sticky in the middle of the page.
On the Dano amp, I would use the Fender tweed volume and tone control after the input tube, just a little more versatile. A waste of a 6SJ7 in the splitter spot, it is set up in triode mode and the cathodyne inverter has a gain of one A 6SQ7 would do with normal 1.5k bias resistor. The schematic looks wrong, the bias resistor on the 6sj7 splitter of 15k looks too high. The 2.2M resistor on the first stage probably should not be coming from the lower half of the splitter but from a power supply node, most likely from the same point as the plate resistor. If you are not doing the tremolo then the associated set of 0.01uF and 390k parts can be omitted. The input pentode is grid leak biased, not much clean if wanted. I thought up a simple switched circuit to change from grid biased to cathode biased quite a while back. See the attached schematics.
If I were to build the amp and since you have a tube for the phase inverter anyway you might want to think of using a dual triode and get some more gain. The Gibson BR-6F has the 6SJ7 up front but has a Paraphase inverter that gives some gain where the cathodyne is unity gain.
Transformers not included in the $199 kit from Boothill.
"Cabinet, Speaker, Tubes and Transformers are NOT included."
How about the Joyo Beal Street?
Supposed to be a head clone of the 5e3.
I have a therdrail 5e3 that was pretty cheap for a Tweed Deluxe- but still gonna run you $600 or so.
Aha, iron=transformers, got it. So you need a power transformer and output transformer? What's a set of those cost, for a small amp like this? Another $100?
Depending on brand, $100-$250 for the set. That's before shipping ($20?, they're heavy)
Wow, thank you! You actually answered a few questions I was mulling over myself already. In the Dano inspired schematic, what triode are you using in the PI? A 6SQ7?
wow, thats a big price spread. So i guess that means they're not all the same
The cheapest, most commonly available are the Classictone transformers. I used those on a 5E3 I built and that amp is still far and away the best sounding I have - not that I have as many as some guys.
It means one brand is much more expensive than all the others, at least when selling to individuals (apparently they have steep quantity price breaks). Pretty much all the rest are in the same price range at $80-100 for a 5e3 transformer set, with some variation due to additional cost for features like 220v PT or multiple impedance options on the OT. A lot of people interpret the price difference as meaning that the notoriously expensive brand is the best, YMMV on that.
I was lucky and bought a 5E3 for 150$.
Someone had failed at putting it together and sold it as it was.
Lots of cold solderjoints, some shorts between leads and chassis and the power tranny was hooked up wrong.
I had to get a set of 6v6s for it and change a few caps, so it cost me about 200$ total.
Nice! I'll give you $155!
I like the before and after shots. Nice work.