Which Pass amp?!

[starbender]

Removed one fqa19n20 and measured.

G-S infinite
S-G infinite
S-D 0.6v

In circuit g-s and s-g shows more than 0.2v. Increasing constantly...

 

[Zen Mod]

in which circuit?

test circuit(s) I posted in #38?

for JFet testing you can use battery of 9V or 12V (UPS Accu , for instance)

for Mosfets , you must use more capable PSU - at least 500mA current capable

say that 12V Accu is good enough , again

 

[starbender]

in which circuit?

test circuit(s) I posted in #38?

for JFet testing you can use battery of 9V or 12V (UPC Accu , for instance)

for Mosfets , you must use more capable PSU - at least 500mA current capable

say that 12V Accu is good enough , again

Diode test mode. I'll build test circuit tomorrow.

 

[starbender]

Sadly I had to replace all jfets, mosfets and ztx's. Good news is I can safely bias both channels to 0.59V. No hum. But my toroid is making some kind of mechanical noise in every 10sec! Toroid is 18v+18v 500VA. Power supply has 8*22000uf. Heatsinks are 17cm deep, 32cm depth, 4cm fins. Any idea what might be the problem for this mechanical noise from the toroid?

 

[Zen Mod]

if it's not overtightened , you can hope that's some dirt in mains

try connecting to other phase mains outlet

 

[starbender]

Checked toroid. Not overtightened. After 2 hours of playing toroid gets really hot. Also cap banks. I need to drill some wenting holes at the top. I guess..

 

[Zen Mod]

in case that , after obtaining proper ventilation, xformer still buzzes and it's more than just luke warm , counting on eenyweeny 110VA consumption (both channels) ...... ask for replacement xformer or find another vendor

 

[6L6]

Checked toroid. Not overtightened. After 2 hours of playing toroid gets really hot. Also cap banks. I need to drill some wenting holes at the top. I guess..

Please post some well-lit, in-focus photos of your amp.

 

[starbender]

I realized toroid is not always does that mechanical noise. If I power on right now, if it's begin to make mechanical noise, it will continue 'till I power off the amp. But if it's not doing this when I power on, it will not have any mechanical noise at all 'till power off. Strange...

I tried f5 with B1 pre. Got a pair of celestion 332. I have to turn volume to almost maximum for decent sound level. Also tried 94dB old bookshelf speakers. Little bit better, but volume is not enough. At least to me

Rail voltages are 24v. Volume pot at the B1 is 50K carbon.

Pics (sorry for messy build )

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

 

[6L6]

Try reversing the black leads on the right rectifier bridge. Yes, it's AC, but it may help.

Also, where is mains AC safety earth? Is it not photographed?

Is PSU lifted off chassis by CL-60 from GND to chassis?

 

[wdecho]

Do you suppose it may just be expansion and contractions of your heat sinks. I noticed on my amp with the Aleph 30 it made some clicking noises as it heated up but not enough to worry about but I knew it was the heat sinks probably where they connect up to the front and back panels. My F6 runs cooler and does not do it in the same case. I just swapped boards instead of buying another case. Tighten all the connections where the heat sinks meet the panels

Nice build!

 

[starbender]

Try reversing the black leads on the right rectifier bridge. Yes, it's AC, but it may help.

Also, where is mains AC safety earth? Is it not photographed?

Is PSU lifted off chassis by CL-60 from GND to chassis?

I'll try reversing the black leads.

Safety earth&cl-60 not connected. Yet!

I'm curious, why sound level is so low, even with full volume? Right now I'm listening tripath 2021 amp with the same speakers while I'm working on this F5. Sound level is more than enought even at pot at 10-11 o'clock position. Ta2021 is max 13W or something. I know it may have more gain. Is this cause that much of difference? I'll have to dial the pot to 3-4 o'clock position to get the same sound level with f5.

I wonder, did I done something wrong?

Ps; While checking voltages I realized rail voltage for both channel drops to 22.3V dc. With zero bias it was solid 24V. Also secondaries has 18v ac before bridge. After bridge it's 22.3v dc..

 

[starbender]

It seems voltage drop under load is more than normal

Last night I decided to replace rail & speaker internal cables. Used thick solid core copper wire. It seems thick wire is better. Overall sound improved. Or I'm fooling myself

Anyway; I got only one concern; heat! I cannot touch heatsinks more than 2-3 seconds. It gets really hot. Also Transformer and cap banks heats a lot too. Every mosfet has 17cm*16cm*4cm heatsinks. I think it's enought for 1.3A bias? At least all suggested heatsinks for F5 more or less same size as mine?

Also, I couldn't stop periodic mechanical noise from transformer. Weird thing is; it does that randomly.

An externally hosted image should be here but it was not working when we last tested it.

 

[Zen Mod]

you need air through case

if drilling holes/slits is outa question now , put 15mm spacers (along with longer screws) between both front and back plate and rest of case , to make slots for air

you can do similar with top plate , maybe even bottom one

be inventive ......

 

[starbender]

Zen, I noticed something. Capacitors which close to transformer now touching each other. Outer cap bank still has 4-5mm distance from each other. Total playing hour is more or less 3-4 hour... Still...

I'm using it without top cover to check heat dissipation and transformer&cap bank heat. I'll drill 'lots' of holes at the top. If its not enough I'll drill some more at the bottom.

Note : In here room temperature are close to 32C.

 

[6L6]

You must drill holes in bottom as well - fresh air must get into case, hot air to escape.

What is voltage drop across 0.47R source resistors on amp PCB?

 

[starbender]

You mean bias voltage? If so; it's 0.59v..

 

[Halair]

You must drill holes in bottom as well - fresh air must get into case, hot air to escape.

...and more open surface area on top lid compared to bottom promote better airflow through the chassis.

 

[6L6]

if drilling holes/slits is out of the question now , put 15mm spacers (along with longer screws) between both front and back plate and rest of case , to make slots for air

Do this.

Did you reverse the black transformer secondaries as asked?

 

[starbender]

Umm... Not yet