The Amp Garage

All the tanks of the originals were open to the wood they were mounted on. Never met some kind of additional metal shield in an original. From the mid to late 90' I've rebuilt several Fender SF Bassman 135 heads. The left side became Fender Blackface Clean, the right side Dumble OD - both channels ...

There is some hum when I increase the Return pot so now I'll have to work on that. The Reverb pan's output has to be far away from the PT, otherwise it might pick up some hum from the PT's stray field. In combo cases no prob, but in head shells the pan sometimes comes terrible close to the PT. Some...

[quote="Fischerman"]When I input a 880Hz/100mV signal (true rms) to the amp and turn up the Volume to a reasonable level I have ~160mVac signal at the 12AT7 grid. /quote] After the plate of V2b - what's just separated by a cap from V4's grid - with 100mV input level should occur somewhat about 20,00...

Tubes hanging upside down is a relict from typical combo amp design, so that you haven't to creep on the floor, to dial the controls. Then they've adapted it for heads. But it's in fact a drastic downside, when 'hanginmg upside down' output tubes are heating up the chassis and all the components ins...

I don't know, what you took from my recommendations above.

Can you post an updated schem at least of the preamp section including the reverb circuit? Then maybe I can be of some help.

Larry

fabiomayo wrote:I have to check the jack input wiring... There may be a mistake there

Larry

Is it my eyes, that I couldn't find any pot in the BOM?
Or are they really missing there?

Larry

Don't forget the ERO/RoedersteinMKT1813 Compared to the Mallory 150's they do have about the same sweet highs, do have a slightly better mid pronouncation and are not as diffus in the lows as the Mallory 150's Try some of the brown polyester caps from Panasonic or NTE while your at it. :wink: I've n...

The gain out of the two cascaded recocery stages will be plenty and you even don't need cathode bypass caps on any of the V3 cathodes. Also a bright cap IMO isn't necessary across the reverb level pot! With the deep switch the 100K's are ok, but the tail then has to be diminished to about 3.3K...3.9...

Does it also make a difference, at what time you fire up the amp the first time? At waxing moon? At waning moon? Did you already know, that especially violet wires become better, when you put them for one night on the grass outside the house at full moon? But don't do it, when in your area werewolve...

Fabio, is the hum gone with a guitar plugged into the input?

If so, then simply ground the switch contact at the tip of the input jack, so that the input is grounded, when no guitar cord is plugged in!

On your photo I neither can see a cable there, nor a solder joint

Larry

what is a Pacific transformer story..... Once upon a time... :roll: Oh sorry! Seems, that I already forgot the rest of the story. or are they just.....trannys? No, they are monsters, which smoke cigarets w/o filter, eat little children and don't donate their skins to the butchers 8) BTW: Usually pe...

Many thanks for this. When you looked into this amp did you notice what value the channel volume pots and the global master volume was (I would expect 1MA)? And what value NFB resistor did Bogner use (given the fact that he virtually copied the 1959/2203 I would expect anything from 47k-100k)? Sorr...

In the right schem and the one on bottom the caps always are in series w/ the resistors, no matter, where the switch is switched to. And the switch then simply is switching both/none/one R/C-conjunction to ground. In the left schem (yours) the switch either doesn't connect the caps anywhere, or it's...

It's IMO not the PT, but the OT! Cutting out and kicking back in wouldn't happen so quick w/ an intermitting short in the PT due to the storage in the filter caps. But the suddenly dropping B+ might be caused by an intermitting short between primary & secondary of the OT, since the secondary nearly ...