Blackstar ht40 No Sound

[Chuck H]

Kudos to those who called out the in circuit fuses. And kudos to Perkinsman's attentive cooperation.

[Perkinsman]

Thanks Jazz, I’ve seen that bias procedure but this HT40 is measured at TP10, not across d36. It actually has “50mV” silkscreened at TP10.

[Jazz P Bass]

Truthfully, I posted the procedure more for the balance adjust.

[nosaj]

Truthfully, I posted the procedure more for the balance adjust.

It was in post 12.

nosaj

[Enzo]

Perk, PLEASE look at your schematic. TP10 IS across D36.

TP10 is at the cathode of the power tubes, and from there to ground are a 1 ohm resistor R217, and the parallel D36. The two descriptions refer to the same thing.

[Randall]

I'm glad this was resolved, but sweet Jesus this was a fricking long way to get to a bad fuse. I mean really?

[nosaj]

I'm glad this was resolved, but sweet Jesus this was a fricking long way to get to a bad fuse. I mean really?

Patience grasshopper patience is all we've got in I've had plenty of moments as . Sometimes because learning can be scary when you're unsure of yourself.
Nosaj

[Enzo]

SOmetimes it is hard to get them to take a step back and see what they are looking at, rather than focussing on each part.

[Mick Bailey]

Well I did say in post #6 to check if he had the correct voltages on the output tubes......

I would still check the PI MOSFETS as well, though. I've not had one of these amps that didn't leak and need fixing. caught early enough it can save the amp.

[Perkinsman]

I just installed the new fuse holder (pia!, since the board needs to be pulled). I'm not familiar enough with this amp to know whether the master needs to be turned up in order to increase the clean volume or is the clean independent. Before i put this back into the cab, id like to check voltages, since the volume seems low. Does anyone have the expected voltages for this amp, they're not on the schematic. Plates on v1 pins 1/6 preamp tubes approx 140vdc & v2 1/6 200vdc.

[Enzo]

We usually do not see high voltages on drawings. They vary a LOT. If we had a 480v B+, for every volt the mains changes, your B+ changes 4v. So if your mains goes from 119v to 125v, a 6v change, your B+ will rise 24v.

The thing is, these are just guitar amps, nothing precision. It would be a total coincidence if a drawing said 438v B+ and yours was exactly that. What to worry about is whether the power supply voltage is even present or not. My amp will work fine with B+ or 480, 500, 520v. It won't work with zero volts there. And if your 500v supply reads more like 250v, then a problem exists. B+ half what you expect? First place to look is for a filter cap not working, so you have TONs of ripple.

When I look at preamp tubes, I check the plate voltages. Hell I usually just go down the row and check them all, takes a few seconds. I expect to see three things. If I find the full B+ voltage there, then I know the tube is not conducting (or it is a cathode follower stage.). If I find 100-200v, then it seems the tube is working. If I see zero volts on a plate, then there is either no B+ of the plate resistor is open. Or a connection to it is open.

Next I check all the cathodes. Pins 3 and 8 on a 12AX7. If I see zero volts, the tube is not conducting. I expect a volt or two usually. SOmetimes several volts. Exception is cathode followers or split load stages. Higher voltages there. WHy does a tube not conduct? Most often because the heater is not working. Almost never the tube's fault.

[Jazz P Bass]

The Master Volume is just that.
"15. Master Volume
This controls the overall volume of your amplifier. Turning it clockwise increases the
volume."
It is a 'post preamp' control.
https://blackstaramps.com/pdf/handbo...0-handbook.pdf

[Perkinsman]

The Master Volume is just that.
"15. Master Volume
This controls the overall volume of your amplifier. Turning it clockwise increases the
volume."
It is a 'post preamp' control.
https://blackstaramps.com/pdf/handbo...0-handbook.pdf

Not sure what post preamp means......just trying to find out whether this amp should get rocking loud when turning just the Volume up or does it require the Master to be turned up before getting significantly loud.

[g1]

What post preamp means is everything goes through it. So yes, you have to turn it up even for the clean preamp channel.

[Chuck H]

Not sure what post preamp means......just trying to find out whether this amp should get rocking loud when turning just the Volume up or does it require the Master to be turned up before getting significantly loud.

This seems to be a conundrum for a lot of players.

The preamp has only so much headroom. The more you turn it up, the less it has. So if you wish to take advantage of headroom you must have the highest volume allowance already available when turning up the preamp volume. That means you must have the master volume at maximum setting for the loudest clean preamp signal.

The preamp volume GOES THROUGH the master volume to get to the amplifiers output circuit. So if the master volume is low then the it limits the preamp volume. Or headroom. Not exactly the same thing but sort of for this purpose.