i had a moment today so i powered it up, R113 started to smoke so i guess that the heatsink was slightly underrated, but ill chaeck up on it if i get som time this week

Quote from: Enzo on February 20, 2016, 06:14:35 PM
Thermal switch?  Do you mean the thermal fuse inside the transformer?  That is usually not in a schematic because it is not a separate part, it is part of the transformer.

i was referring to TSA1....was aware that the transformer had a thermal fuse inside i is shown on the 2nd page, but i had i confused with one of the primary windings, i feel a bit stupid now.

when i get it up and running i wonder what might burn.

Quote from: phatt on February 21, 2016, 05:49:50 AM
And don't forget TSA1 (Thermal cutout) mounted on the heat sink as well.
I worked on one of these amplifiers a while back,,, watch out for heat issues on R172/173 and R160/161.
Those were running so hot they had burned the PCB and de-laminated the traces. (not much R/D from Fender design team went into this one :loco)
CR56/57 were also overheating. Expect finger burns from them.
If I recall correctly, I had to remount those parts off board.
R37,38,39 (although not as hot) were raised higher off the PCB to keep the heat off the PCB.

Phil.

when i first opened it i thought the heatsink to be somewhat underrated event though it is directly on chassis

oh i see that now i had it confused with the thermal switch, which isn't shown in the schematic, but is in series with fuse and thermistor.

i know they are far from 100% efficient but i often seen somewhere 150-200W for 100W out but then again the heater supply dissipates about 7W
i'm in 230 land there are suppliers that offer a replacement but the price is way too high 135 euros plus shipping so i was going for an alternative.
a toroidal equivalent cost about half, but then i would have use a different fuse due to increased inrush maybe a time-lag same rating would do...

hey

Got a fender performer 1000, mains transformer blown.
From the schematic i can see secondaries 60VAC center tapped or 2x30VAC, but what would the current rating be?
The chassis says 300W but that seems excessive, any thoughts?


http://support.fender.com/schematics/guitar_amplifiers/Roc_Pro_1000_schematic.pdf

i have seen angled speakers in a fender bass cab it was a long time ago, i think it was 4x12" and they were all angled towards the center.
the were placed like a cross top speaker pointing down, bottom pointing up, left pointing right, and yes right speaker pointing left.

you should get the complementary buz906 as well

always use complentaries, so when switching to another type change all transistors,

with a quick look this is my guess.
you should look at two current paths
R6, R5 and D2 is one path and R6, R7 and D1 the other.
the diodes are biased by a very weak current  (9-1,6)/(10k+47k)=157µA
if voltage at D2/R5 rises, then Vforward D2 falls and current decreases. and current through D1 increases, therefore voltage across R7 increases.
were talk small variations to avoid cutoff.

i'm shure someone has a some things add or clarify

When you say "a signal will pass through" is it measured with oscilloscope or heard through the speaker?

If you do not have an oscilloscope i would replace the 12ax7 with one that is known to be good.

or:

If you heard sound from instrument channel and not from the mic channel, then everything after the phaseinverter is good, or good enough.
Take an audio probe (a coax cable with a multimeter test probe in one, end and two hooks or clamps in the other end, for signal and one for ground/screen, and a capacitor in the signal path for picking ip audio with a DC offset)

Connect hooks to groung and instrument channel volume pot, apply signal to mic/acc channel and follow this signal path with test probe end.

Use a multimeter test probe with a short pin or insulate it so max 4mm are exposed, limits the possibility for making a short cuircuit.

Usual disclaimer tubes=high voltage=fire death and destruction

Quote from: LeftysquireAm I crazy?

Yes, sane people do not insist on building their own gear, they buy stuff that works...or seems to work.

If you go with kits that are known to be good, I cant see there should be any problems, but test each module independently when finished.

But why do you only want delay/reverb on your clean channel? Thats always a great thing to have...

have fun

Quote from: RolyJust out of personal curiosity whereabouts are you?  Here in Aussie it's nominally 240V single phase and 415V phase-to-phase (and yagotta wonder how anyone could even manage to do that).

I´m im Europe, it 400VAC not 380, it was a Studiomixer power supply, when it was fixed i returned it at the sudio to check i mixer was fried also, and i asked him what had happened... he was goin to put up some new lamps an then everything just went black... some how he had konfused the conductet to the lamp out with L2 and somthing with N, any how hed had 400VAC on all outlets in the listening room, apperently the PSU rectifier bridge protected alot of the equipment.
after the first try he disconnectet everything and returned the lights connections as they were to begin with..

often the truth about how stuff breaks is revealed once they are fixed...

i was just looking back in the thread to see what had been tried, and...

Quote from: ogeecheeman on May 07, 2015, 12:38:39 PM
ok.amp comes in-user replaced bridge rectifier.installed backwards.

but why, ?
last time i replaced a rectifier bridge it was because someone applied 380VAC to mains instead of 230...

funny stuff...

What is Vb Q12 & Q13, it is a good idea to measure all three transistor pins when you´re at it.
if R49 or R76 is interrupted ther is no base current for Q12 & Q13, and they will be off.

thanks for the answers, and i am glad that i was on the right track.

my doubt started some time ago when i was reading about a power amp design and it was said to be stable down to 8Ω, and i started to think about it.

hi
I have been wondering about what sets the limit for a power amps load.

example:
if a amp is rated minimal 8Ω and for some reason I want to load it with 4Ω.
lets say its a discrete push-pull with one complementary transistor set, could I then just add another complementary set, and related circuitry?
the above completely ignores that th power supply should be upgraded.

or is it the power supply current capability that limits the amps load impedance?