First build - first problem

[gkwallace]

Going through my start up.
Only rectifier tube installed
Main switch on
Standby on standby
Rectifier glowing
On the standby switch ON terminal, only reading 286v not 340v.
Any ideas?

Thanks in advance for your help

[crgfrench]

What power transformer are you using and how is it wired?

[gkwallace]

What power transformer are you using and how is it wired?

It's a magnetic components classic tone
290, 5 and 6.5v secondary

[gkwallace]

I built the amp following the instructions to the t, without considering the logic.

After reviewing the schematic, all I have to do is see if pins 1 and 7 both have 290v and the filaments/cathode, 4 and 5 are 5v.

Sound correct?

[geoff 1965]

can you confirm which rectifier tube you have?

[TexasTele]

What is the Classictone part number for your power transformer, for example “40-18046”?

[gkwallace]

What is the Classictone part number for your power transformer, for example “40-18046”?

40_18035
EZ81

[geoff 1965]

the ez81 has 6.3 volts on the filaments so you need to swap the yellow/white 5 volt wire for the white 6.3 volt wire.

40-18035.pdf

the schematic shows the correct wires but wrong voltage!

[gkwallace]

the ez81 has 6.3 volts on the filaments so you need to swap the yellow/white 5 volt wire for the white 6.3 volt wire.
40-18035.pdf
the schematic shows the correct wires but wrong voltage!

Your awesome!
Thanks!

[gkwallace]

Not sure if there was actually a problem now. Might have been the voltages on schematic that were wrong.
I decided to just go for it and it sounds great. I have an issue with one of the input jacks on the clean channel, but everything else works as expected.

[geoff 1965]

so now you have all the tubes in what's your initial B+ at pin3 of the ez81?
there are voltage charts in the downloads section you can fill in and post.

[crgfrench]

It looks like that BYOC schematic has the 5V tap listed in error.

[gkwallace]

so now you have all the tubes in what's your initial B+ at pin3 of the ez81?
there are voltage charts in the downloads section you can fill in and post.

Cool. I'll do that.
Got sidetracked with a new oscilloscope today.

[gkwallace]

so now you have all the tubes in what's your initial B+ at pin3 of the ez81?
there are voltage charts in the downloads section you can fill in and post.

Still have 284v at pin 3.
It sounds good but the cranked gain sounds loose or flabby, if that makes any sense.
Clean sounds beautiful.

The voltage at the filliment is 10v, should be 6.3.


I'd like to figure this out.

[geoff 1965]

that's not enough,you're B+ should be in the region of 350 VDC with the 290-0-290 supply. what is your primary mains voltage 120 or 240V, and have you checked the voltage on pins 1 & 7 of the rectifier?
it helps when troubleshooting if you can post the layout you used and some pics of your amps internals.
is the 10volt filament voltage you measured on the ez81?
i would'nt leave the amp on for long at this stage and make sure your speaker is plugged in if you don't have a dummy load or you could damage the output transformer.

[gkwallace]

I'll take some pictures and get some voltages asap

[gkwallace]

IMG_20191212_095416.jpg

Pin 1 and 7 are 300vac
Pin 3 is 284vdc
Pins 4 and 5 together are 10.5v with power on, tube installed.
110 primary

[geoff 1965]

do you have a spare ez81 to try?
you could unplug the ez81 and see what the voltage is on pins 4 &5 to see if its drops to 6.3V.

[gkwallace]

I ordered one today. I'll update on Monday when it comes.
Meanwhile, I'll resolder all relevant connections and pray.

[JMPGuitars]

Pins 4 and 5 together are 10.5v with power on, tube installed.
110 primary

Measure your heater voltage relative to ground.