Blues junior build. No sound

[Brandonallen1212]

So I built this blues junior clone based on Dougs design. I used the power transformer from my existing blues junior and I am not getting any sound out of the amp whatsoever. I tested the resistance between all of the windings and what I found was that all the secondary windings resistance fell within spec, but the primary winding read about 9 ohms. The data sheet says it should be 4.7 ohms +/- 20%. I am almost 100% larger. Is this enough of a variance to cause the amp to produce no sound at all? I am also getting much lower voltage then I am supposed to be getting from my high voltage secondary, and my heater wires. They are about 60-80% lower voltages then my schematic calls for, if I remember correctly. Is this decreased voltage in the secondary caused by the increased resistance in the primary? And are these variances enough to cause nothing at all to come out of the speaker?

[sluckey]

And are these variances enough to cause nothing at all to come out of the speaker?

Not likely. Wiring error is number 1 suspect.

[thetragichero]

if there is a short in the primary the reflected voltages on the secondary will be lower. if your filaments aren't receiving appropriate voltage that would certainly cause no sound

[PRR]

> The data sheet says

Where can I see that?

IMHE, 7 Ohms is a bit low (for 117V wall) but not wrong.

VOLTAGE readings may be revealing also.

NO output, even ear on grill in a sound-dark closet, is usually miswired speaker jack. There's always hiss and hum.

[EL34]

Did you follow the instructions for this build on the library page?
https://el34world.com/schematics.htm#Hoffman_Blues_Junior_Conversion

This document is important
https://el34world.com/Hoffman/instructions.htm


Then in that document, this link is important
How to double check your amp wiring and find things you missed
https://el34world.com/Forum/index.php?topic=17701.0

[Brandonallen1212]

Yes I read all of the attachments. I will make a 3rd pass checking app wiring to make sure I didn’t miss anything. What would cause the high voltage leads coming directly off of the secondary winding of the power trans to have significantly lower voltage then rated? The high voltage and the Filaments are both lower then they should be

[thetragichero]

you've tested their ac voltage unconnected from the rest of the amp?

[sluckey]

Did the original Blues Junior work properly before you built the Hoffman version? Did you measure any voltages on the original?

Rather than just saying voltages are lower than they should be, give us some actual measured voltage readings for B+, Z, X, Y and also filament voltage.

[Brandonallen1212]

Power transformer secondary.
Red wires 120 vac
Brown 23 vac
Filament (green) 3.56 vac

B+ 340 vdc
Z 326 Vdc
Y 309 vdc
X 308 vdc

When firing up to get these readings I found that the filaments are now not even lighting up on v1 and v2. Going back through to carefully trace the entire circuit one more time and check solder joints

[Brandonallen1212]

I forgot to mention I was having issues with this amp before I decided to rebuild it.

[sluckey]

Those DC voltages all look fine. I bet you are measuring the PT red leads referenced to chassis. Don't do that. You'll get the correct reading only with one meter probe on a red wire and the other meter probe on the other red lead. IOW, measure voltage ***BETWEEN*** the red wires. Same for the green filament wires.

[Brandonallen1212]

That is exactly what I was doing. I am tracing and testing all components again and have found the 120k resistor on the master volume pot is not giving a resistance on my multimeter as well as the 10k on the feedback loop from the meat control. I am just going to assume they are bad and replace them. What would cause the filaments on v1 and v2 to so lighting up? I checked all connections to sockets including filament wires. They have be one and have done a pulsing thing and I haven’t been able to find any other info on the web. Thanks so much

[acheld]

Hey there.  Pictures of the connections to all of the wires coming from your power transformer would be really helpful to help troubleshoot.

What problems were you having with your amp before you rebuilt it?

[sluckey]

I'm ***ASSUMING*** your filament string first goes to V5, then V4, V3, V2, and V1. If so, the correct way to troubleshoot dead filaments is to start at the first tube in the lineup, in this example, V5. But since you say only V1 and V2 are unlit, let's start at V3.

Be sure pins 4 and 5 are jumpered together on V1, V2, and V3 sockets. Then set meter to measure AC volts. Connect one probe to pin 4/5 of V3 and connect the other meter probe to pin 9 of V3. You should measure 6.3VAC. Now repeat this check at V2 socket. I bet you will find you don't have 6.3VAC. So, look for a bad connection on either V2 socket, V3 socket, or a broken wire(s) between V3 and V2.

BTW, if V1 and/or V2 filaments are not lit up, you will have NO sound from the amp other than maybe a little power supply hum.