Tube circuit transplant for a 90's Fender Bronco

[@jazzdrumguy5044]

I am picking one of these tweed ones up tomorrow. I am looking forward to it. The harmonica sounds incredible from this amp! I sure wish it was a tube, but it looks so cool, I will deal with it!

[@franckrichard8077]

I am lucky enough to have found a Bronco in tweed finish, in a very clean state. I intend to change the speaker with a Weber or a jensen and to put some shellac on the cabinet. I am not very found of the lattest ToneMaster amps from Fender : too many planned obsolescence components in them. I like the stuff I can repair myself.

[@jazzdrumguy5044]

I have a real Twin Reverb and bought my teen a T.M. Twin Reverb. It is a pretty sweet amp and super light! So far so good. The real Twin is great, but a pain to take to his gigs.....I got a killer deal used but like new, so if anything happens to it, that's fine.....

[@robnic52]

Love the amp, nicely played harmonica, the vibe of Little Walter coming though loud n' clear. Seems there's a healthy blues community in Australia.

[@TheZedvox]

Thanks Rob. Yeah, plenty of good blues players down here. One of our Sydney bands the Foreday Riders has been going since 1967, still hot to trot.

[@JustSamOfficial]

Nice one Mark

[@TheZedvox]

Thanks 👍

[@johnmac8084]

Thanks for not being too proud to show us the mistakes as well 😀

[@TheZedvox]

Thanks John. Mistakes help us learn.

[@johnmac8084]

@@TheZedvox Exactly Mark

[@CC-te5zf]

Learned much! Thanks!

[@TheZedvox]

Glad it was helpful!

[@KeritechElectronics]

I love these kinds of projects - get a lovely looking amp with crap inside, upcycle it with tubes. Did a bunch of them. BTW personally I'm rather skeptical about using a tube rectifier on single ended or class A push pull amps, unless we're talking about making the design oldschool-ish, true to the good ol' days etc. I'd use a switchable rectifier for a class AB or B PP amp and a solid state one for anything class A. Methodic approach is THE way of building anything good... Slow and steady wins the race. Harmonica players' amps... back in the days when I was working on some projects together with Piotr Stanisz of Black Dog Amplification, I recall him making a custom harmonica amp.

[@TheZedvox]

Thanks Keri. I'm always happy to learn from amp builders with a lot of experience.

[@jamesvandamme7786]

Just remember the diodes come on instantly with no tube load, so you've got a lot of voltage on those filter caps, and a big surge current. A tube rectifier will do the same thing but slower; the voltage will peak then settle down as the output tube comes on.

[@KeritechElectronics]

@@jamesvandamme7786 yes, it all depends on the power supply's design - direct vs indirect heating of the rectifier tube, filter cap capacitance, type of filtering element (R or L) etc.

[@russellesimonetta3835]

I was always interested in a design from Weber Amps,, it's a 15 watt princeton based single ended running a KT 66. It was designed as a harmonica amp. You could just follow fender style ground schemes. Each stage has it's own dedicated ground . Sometimes good enough beats theoritical perfect.

[@TheZedvox]

That sounds very cool. I will check that out. Thanks.

[@russellesimonetta3835]

Champamazoo!

[@TheZedvox]

Haha good one.

[@moodyga40]

i notice you had the filters around the wrong way we have all been there, you can make a centre tap using 2 x 1N4007 diode i am using this method in my 300 B stereo amp i am building now

[@TheZedvox]

Thanks Ian. Always good to hear from a wiser head.

[@jojokeo]

You could've/should've ran the power resistor between the rectifier and Node A. Assuming appx. 0.05A draw * 1K5 = 75V dropped across it as a starting point without doing a bunch of math. Then calc out (75*75)/1K5= 3.75watts and double for safety = 7.5w rated resistor. So you're fine with both. You could've got your lower voltage w/out the zener network? Another option is to wire in an additional Filter Cap + dropping resistor prior to node A yielding improved filtration also. FYI, never run voltage to ground through a resistor only rather create a voltage divider network w/ a cap on the lower half of the divider network. This is commonly done to the heater/filaments elevating them above ground yielding quieter floor noise if/when needed.

[@TheZedvox]

Plenty of good info there. Many thanks. I did consider another C+R before node A but lacked the necessary real estate.

[@jojokeo]

@@TheZedvox I've got a lot of re-purposed amplifier project designs myself - very fun and satisfying. I've only posted a couple things on youtube but check my channel for a couple. 🙂

[@moodyga40]

so you are making a shunt regulator you should have 15K in series to the Zener's

[@ajhnubia]

a lager value in the cathode of the 6V6 would be best