Is there a 'Blackface' type ~15w clone?

[The Captain]

Have you tried installing a negative feedback loop as per the PR? Look at how the cathode at V2, 3 is wired. I suppose, in the absence of a better suggestion, that the additional gain/layout might be making the amp unstable and some NFB might be of benefit? Be aware that if you fit a NFB loop you may need to reverse the blu/brown wires at 6V6 pins 3.

No I cant say I have- I did notice the differences at pins on V2 on the PR to the 5E3 before doing the changes.. trying to figure this out & applying though as a NFB concept, & as Ive spent nearly 3 weeks trying all these simple applications without success so far, Im reluctant to say- particularly in lieu of all your time and effort to help- that Im totally done in with it now; I did subsequently go over the plans between the 2 circuits at V2 before writing this, but its just not sufficiently clear to me what with different pin links, things going to different component values, some not bypassed, and then changes to the 6V6s too etc.. it'd finally make me go completely insane if I go on; unless there is anything else I can do thats straightforward re applying this tonestack Im afraid its just totally got the better of me Mark. Really appreciate the help of course! Capt.

[MWJB]

At this point the most straightforward thing you can do is pull the tubes, drop the chassis, pack it up & send it to me. I'll either give you an appraisal of what the problem is & the cure, or for an hour's labour isolate it and rectify. Drop me a PM for my work adddress.

[The Captain]

Thats a fine idea thanks indeed- but Im gonna start afresh Mark besides as its a right dog's dinner Id be far too bashful to send what with all my tinkerings!!
So my plan now is the PR circuit using your PT (earlier breakup with PR circuit too?- not so important for now mind), the Jensen, the OT and valves (bar the 5y3) & odd bits/ flog my pine cab + chassis & recoup some £s hopefully.

Qs before I start: the PR bias circuit takes a feed from the 5U4GB's HV at pin 4 to a 100k to drop voltage etc.. as this PT is 508V, is this sufficient to use similarly? (poss Id use a lower dropping r if Im thinking right). Also is the filament's 6.3V pair, at 2.5A, ok for 1x 5u4GB, 2x 6V6- and the 2 extra ~12A*7s?

It'd REALLY clear my head to start anew; Ive learnt a heap from all this so Im confident I can plan it well- eg use all above board wiring/ do a really careful job checking each build step & solder (not that Ive ever had even one bad/ dry one)- and it'll be a right corker.
Thanks for offer Mark- rgds Capt.

[MWJB]

I'd stick with the 100k dropper from the B+ secondary, I'd adjust bias voltage farther down the line, using a trim pot instead of the grounded load resistor in the bias circuit.

If I rember right that PT has a 3A 5v winding? If so that will be fine for the 5U4 BUT... I wouldn't use a 5U4, I'd go straight for the GZ34. Fender switched to 5U4 after bumping up the B+ voltage, to correct it back down again. You don't need to shed any voltage.

2.5A for the filaments will be OK for 2x6V6 (0.9A...0.45A per tube) & 4x12A?7 (1.2A...0.3A per tube). Stock Princeton PTs are typically rated for 2A.

[The Captain]

Thats right, 5V 3A pair and the 6.3V 2.5A filament pair. Great I can crack on with this & a gz34 on the list too; just one part's bugging me (PR schemo's type hard to see).. above 6V6s on this layout, what is this circular 'terminal' component?

http://i102.photobucket.com/albums/m...164_layout.gif

Thanks Capt

[TD_Madden]

don't know which component you are referring-to, but if it's the one on the left-center...that's the top of the can-capacitor.....

[The Captain]

Can capacitor eh.. Ive never seen the like before, I guess this is the filter capacitor? The 4 tags on the top- are these usually marked with a symbol (seems there's a triangle/ square etc on layout) on the cap top so you know what's what?

[MWJB]

Yes, the cap body is usually engraved with the legend.

I prefer to not use cap cans so I can run my grounds to where they need to go.

[The Captain]

Ok, so I need a '4x 20 multicapcan' with 4 solder lugs.. none from the usual sources from UK/ EU. Is there any capcan I could use instead? Is the reason these blasted things are used only that ~4x 20uf axials would just take up too much space?

[MWJB]

If you're using the Torres PT you will only have a B+ of 330v-ish, 450v e-caps will be fine, like the Evox Rifas from Bluebell. Use 47uf for the main filters.

Cap cans were a time/costsaver for mass produced amps, they are often a cause of hum. There is no reason for a private builder to use them unless a customer requests it to keep a vintage amp looking original (even then I still wouldn't).

[The Captain]

I dont think I'll have room Mark: I plan the BF Princeton no-verb now in a Bluebell 13.5" chassis to mount 'upright' a la 5E3 in the cab, just. I'd have to build another cab to use a 17" for eg to get a PR in, or to use 4 Evox axials- space really tight. Weber do a can-cap which the same PT I had in the 5E3 uses, but with its lower 540v HV pair (tho the bias board takes a dedicated 45v feed from the PT not pinching it off the ~GZ34's pin 4 like Im going to do), so, the torres PT being not far off @ 508v means I could use the same 4x20uf can-cap.. unless Im talking baloney of course!

I presume the Princeton Amp AA64 is just the PReverb minus the reverb- it seems to have 2 less 12A*7 tubes though. I hoped to add a MVol to the PR at a later date too, can this idea still apply to the Princeton no-verb do you think?

Any comments very welcome, Capatain

[black_labb]

I was about to say, do as Stokes said, build a BF preamp, and a dual champish power section, two tubes, with one who can be switched out for less volume. It has been done before iirc.

Bye.

Max.

why not put a vol pot on each, then you can adjust each volume to suit your needs. pump one up for overdrive, keep them both equal for a cleaner sound and mix them around a bit. why not change the tube type to get different sounds?

[Satamax]

why not put a vol pot on each, then you can adjust each volume to suit your needs. ?

How would you stop them interacting with each other? Otherwise we would have a real nice way of quietening big multivalve amps

[black_labb]

How would you stop them interacting with each other? Otherwise we would have a real nice way of quietening big multivalve amps

im just looking at simple designs for myself at the moment, but my thought was to have the power tubes in paralell each with their own pre amp stage before the pot. you could have one preamp stage before the splitting of the signal. maye using a pot to adjust the gain on the first preamp stage for when there isnt any signal going into one of the signal paths. it might not be perfect, but it would be alot more adjustable in terms of sound.

i dont know much about amps, but it seems feasable to me...