Quote from: J M Fahey on November 27, 2015, 09:58:01 PM
The power amp is reasonable, but avoid the multiplier if you need any power, get HV from a proper HV winding.
Bias with a scope until you get rid of the crossover notch, we are talking very low current anyway, almost pure Class B

What about something like this smps with the MC34063 for the high voltage?

http://www.imajeenyus.com/electronics/20111010_40-400V_supply/index.shtml

And if I'm not wrong, you could use another chip to get -12v. I bet you could make it all run off a single 12v gel battery or a cheap laptop-type supply.

[EDIT]

I have run some simulations of a similar circuit on Proteus and I got to the following results, with the output adjusted for 280v with no load.

- 5K Ohms load: 280v, 56mA (15.68 Watts)


- 3K Ohms load: 247v, 82.5mA (20.37 Watts)


So, in theory, this could be a suitable power supply for small tube projects (probably up to 10w, depending on the tubes used).

Quote from: mexicanyella on November 22, 2015, 05:16:33 PM
I've never played through a honeytone before, but I have to wonder how it'd sound as a line-level ouput device, driving a larger power amp and some big speakers...I had some fun doing before with some small practice amps, a rack power amp and Marshall 4 x 12 cabs. Might be something fun to try...rebuilding it as a line-out preamp kind of device.

I think the best way to do that would be to lift the cap right before the power-amp input, and add a switching jack that switches it back into the circuit when nothing is connected to it, so you're taking your output from the preamp only.
I wouldn't recommend trying to get a line out from the power amp, as it's a bridged circuit.

The amp by itself is fairly capable of driving large cabs. If you have a regulated 12v @ 1A adapter (I'm pretty sure you could use as low as 500mA, but 1A seems more common), that will squeeze about 2w out of this unit, as long as you keep the load at 8 ohms. That's pretty decently loud for home and recording.

Here's a service tip: If your version of this amp has a speaker marked "2W", NEVER crank it. You'll fry the speaker and take the power amp chip with it.

I did just that and ended up having to change the TDA7052, but I couldn't find the sufix-less version so I got the 7052-B.
To use that model of the chip in this amp, remove the 4K7 pull-down resistor on the chip's input in the circuit board, and add a 1M resistor in parallel with a 1uF to ground from pin 4.
I don't know if that'll work with the 7052-A, since I was unable to find it.

Also, make sure to get the magnet height of the substitue speaker you're ordering, and that it matches as close to the original as possible, or less (in case of an alnico one).
If it's too tall, it'll hit the "battery box" and you'll have to cut part of it to fit the speaker, which will make the battery impossible to fit! Not a good trade.

Hope this is helpful for the future!

Thanks J M Fahey and teemuk! I see it clearly now. Very clever, I must say!

I really like both the preamp and phase-inverter designs on this amp. They put many ideas in my head... too many!  :duh

I am SO going to steal take inspiration from that phase inverter!

Now what kinda bugs me is that the preamp uses diodes for most of the overdrive sound. I wonder if the triodes get distorted at all?

Quote from: Enzo on November 04, 2015, 06:05:57 PM

if it works and sounds good, I have no idea why you'd call it a paper weight.

Exactly.
Doesn't matter if it's tubes, transistors, op-amps, digital emulation, or whatever they come up with next. What matters is that it's good to you.

Quote from: mguzzo on October 16, 2015, 11:43:58 AM
I have a PF10 as well, I've been thinking about a speaker mod.
Instead of going "bigger" I was going to go "better" with a Jensen 6" vintage alnico
https://www.jensentone.com/vintage_alnico/p6v

I think with a sensitivity of almost 92 dB it would really open up the capability. I haven't found any data sheet on the stock Bulldog speaker.

I'd say go for it! Guitar speakers are hard to come by where I live so I can't really say if it would be a good match for the PF10 or not, but I've always heard good things about Jensen speakers! Speaking of them, their MOD 5-30 has always intrigued me. I wonder how it sounds...

It would be really cool if you could use a RGB LED on those pots and it changed color depending on the level of the control!

Quote from: joecool85 on October 05, 2015, 08:04:32 PM
I did this on my K-20X.  For a few years I played through a 1x10 cab, then sold it when I didn't have the space/need for it.  Now I'm thinking about getting one again.  Since I made a speaker out jack, it's just a matter of buying or building a cab and I'm all set.

Exactly! It's much more practical than taking ou the speaker and cutting a bigger hole for the new one.
You could easily take it to small gigs or practice and plug in a large cab. Now, if you want more power, you can always change the power I.C. + power Transformer, but honestly I think just a larger cab will be more than enough.
These small combo amp speakers aren't usually as efficient as "proper" guitar speakers.

I've recently acquired one of these amps and I noticed that it does a strange, noise-gate-y sound as a note decays or you turn down the guitar's volume while on the high gain setting.
I'll do some measurements soon and report them here, because I don't think that's supposed to happen, and if I can find the problem it'll be helpful to other people who might encounter the same issue.

I'd personally just add a speaker out to the amp. The original speaker sounds fine for practice.
Plus, that allows you to experiment with cab combinatons that would work better for your style (or your needs for loudness).

Here's a stripboard layout I'll be building, most likely today, after work. Not as neatly done as Plautz's but It'll work:



In that layout, the pots are supposed to be facing upwards (aka viewer's direction), and I'll use rigid copper wires to connect them to the circuit board.

I only have DPDT switches, so I'll be using this neat circuit (already included in the stripboard) to switch the LED on and off:



P.s.: I just noticed the gain pot (left) is marked as "10k Volume" instead of 1k. Oops. You know my secret now, I copy/paste a lot.

Quote from: Enzo on August 17, 2015, 11:36:49 PM
If you are committed to the TBA chip, cool.  I think in my head I was kinda thinking a more versatile power source would allow more powerful amp chips, like a TDA2030-40-50.

Not really looking into that much output at the moment. I can barely use this amp through my 8" Vox Bulldog without getting told to turn down the volume!

Plus, I'm planning on having this amp built into that Bulldog's cab in the future (or another version of it, perhaps with a Vox stack?) with a 12v 2.3A sealed battery in it, since I would like to take it to a local trimestral event.
Last time I went to it, I used my trusty Honeytone, but next time I wanna take something I actually made by myself.

Quote from: Enzo on August 17, 2015, 12:06:58 PM
That is the idea, but we'd have to study the information.  Engineer types like Juan would know more than I on that.

Considering the info on the TBA820's Datasheet, it can deliver 2w on 8R at 12v. That would be 500mA.
The booster circuit can deliver up to 1A with Vin of 5v and Vout of 18v.
If we think of losses and say the amp actually uses 750mA, even a 6v sealed battery would be enough to power the circuit with a good 250mA+ to spare.

Quote from: Enzo on August 17, 2015, 09:13:25 AM
Or a 12v gel-cell running a switcher.  Then the circuit voltage is not tied to battery voltage.  Those batteries have a lot of juice.

Perhaps one of these? https://www.pololu.com/product/2571