Millet Hybrid - only one channel working

[nyjets28]

I really need some help. I purchased a Millet Hybrid off another user here and I'm connecting it from my EMU-0404 usb via two 1/4" to RCA's. but only one channel is working. i tried to switching the plugs and all kinds of combinations but nothing is working. the left and right seem to work individually because when i slowly plug in the headphones, the sound comes in the left first and then the right. but once it's fully plugged in, only right side comes out.

i don't think the seller sold me a busted unit because he has good feedback here. please help! this is my first time using a tube amp, so maybe i just am doing something wrong?

 

[tomb]

Quote:

Originally Posted by nyjets28 /img/forum/go_quote.gif I really need some help. I purchased a Millet Hybrid off another user here and I'm connecting it from my EMU-0404 usb via two 1/4" to RCA's. but only one channel is working. i tried to switching the plugs and all kinds of combinations but nothing is working. the left and right seem to work individually because when i slowly plug in the headphones, the sound comes in the left first and then the right. but once it's fully plugged in, only right side comes out. i don't think the seller sold me a busted unit because he has good feedback here. please help! this is my first time using a tube amp, so maybe i just am doing something wrong?

First of all, hearing both channels when sliding the headphone jack in means nothing. Both channels on the jack pass by the right amp channel while you're plugging it in.

There could be a number of things going on:
1. Do both tubes light up? Most likely this is true - if I remember correctly, the MH will not work unless both tubes are lit.
2. If you swap tubes, does the working channel follow the tube or does it stay on the right?
3. If both tubes seem to work in the right channel, it's possible the bias got knocked out of adjustment for the left channel. If the bias is not properly set (different for every tube), the tube will not amplify and pass sound.

You might try contacting the seller and see if he'll trouble-shoot it for you.

 

[nyjets28]

i've tried swapping tubes and still only the right channel is working. i think one of the RCA input jacks is actually defective. i'll wait and see what the seller responds. hopefully he does respond. i sent him a pm last week about something else and have yet to hear back.

 

[nyjets28]

is the bias for each different tube? or for the amp itself? is it something that can be set easily?

 

[FallenAngel]

Uhm... the Millett Hybrid needs to be biased when swapping tubes. It's not hard, read the support site. I'm leaning towards tubes not being biased. Maybe something else, but definitely tubes unbiased if you haven't do so yourself.

 

[nyjets28]

the seller still has not gotten back to me yet. so if i don't hear back at the end of this week, i'm not sure what i'm going to do. as of now, i'm thinking of just selling it as is to someone who might actually know how to fix it OR depending on how much it'd cost for someone who knows what they're doing, get it repaired.

i'm just really pissed off about this whole situation because the seller does have good feedback and i emailed him at the beginning of last week (Tuesday if i recall) and still have no response from him, even though based on his posts, he's been on the forum a few times in the past week.

 

[tomb]

This is a thread better posted in the DIY section, but can your remove the top lid and take a photo? At best, you may be able to determine if there's a wire loose on an RCA jack. Or, I may be able to spot something. As FallenAngel and I both have stated, I suspect the tube bias. There's hardly anything that can go wrong with an RCA jack unless it's melted going in. Otherwise, either a wire falls off or it's something else entirely.

If your Millett is using the standard Hammond case, you'll need to remove the four screws on the backplate and the top two screws on the frontplate. Then you pull the backplate down. Grip the top plate on the top and bottom and pull the top plate out of the top slot of the extrusion body. Needless to say, remove the tubes before you do this - but be sure you remember which tube is which when you put them back.

 

[nyjets28]

http://i838.photobucket.com/albums/z...9/100_0070.jpg
http://i838.photobucket.com/albums/z...9/100_0072.jpg

hopefully someone can help me with these pictures. thanks!

 

[tomb]

Quote:

Originally Posted by nyjets28 /img/forum/go_quote.gif http://i838.photobucket.com/albums/z...9/100_0070.jpg http://i838.photobucket.com/albums/z...9/100_0072.jpg hopefully someone can help me with these pictures. thanks!

Can't say I like that grounding scheme, but it won't cause the problems you are experiencing. There's nothing wrong with the RCA jacks, either.

Back to tube biasing, I'm afraid.

Interested in learning how to measure and set that? Got a DMM?

 

[nyjets28]

DMM? Hopefully, if it's a relatively easy fix, I can try during my winter break which will be coming up in a few weeks. Do you think this is something that just occurred during the shipment of the item? if not, i'll be sure to leave the seller some negative feedback; although at this point, i think no matter what i may be doing just that because of the lack of response. i'm gonna keep bugging him till something happens...hopefully i can just fix it

 

[tomb]

DMM = Digital MultiMeter. You only need a $5 one from Harbor Freight - that's good enough to bias the tubes. It's sort of needed on the Millett Hybrid, because this adjustment is needed every time a tube change is made. It's not too difficult to do this, though. Stick the probes in two holes and measure. Turn the adjustment screw (trimmer on the PCB) until you measure 1/2 the power supply voltage at those two holes. There's a set for each channel.

Even if that turns out not to be the cause, the DMM will help you check the rest of the amp. You can compare portions of the right channel circuit with the left channel circuit and isolate where the difference is. That's sort of a DIY-thing, but the opportunity is there if desired.

 

[nyjets28]

so the two holes would be the two RCA inputs? or one RCA input and the HP jack? and also where is the adjustment screw? i'm sorry, i have no DIY experience at all and i'm hoping that this is a relatively easy fix.

thanks so much for the help anyways.

 

[FallenAngel]

Yeah... well, for a Millett Hybrid, you need to bias the tubes whenever you install new ones (and unless you made sure to install the "originals" in their correct Left/Right position, you will have bias every tube you install in the amp). Read the wonderful documentation on the amp, biasing the tubes is very simple. Good luck.

 

[tomb]

Quote:

Originally Posted by nyjets28 /img/forum/go_quote.gif so the two holes would be the two RCA inputs? or one RCA input and the HP jack?

NO. The two holes are on the PCB marked "BIAS TP." There's one pair for each left and right channel. You stick the DMM probes into those two holes and measure for 1/2 the supply voltage. Assuming you're using a 24VDC power source, then you'd adjust the bias for each tube to 12VDC.
Quote:

and also where is the adjustment screw?

These are also on the PCB - again, one for each channel. They are marked R2L and R2R on the PCB. They'll most likely be a little blue square thing standing on end with a tiny brass screw on the top. That's the adjustment screw.
Quote:

i'm sorry, i have no DIY experience at all and i'm hoping that this is a relatively easy fix. thanks so much for the help anyways.

It is very easy. You just need to know where to look and where to stick.

All the details can be found here:
Hybrid Headamp
There's even such a thing as a Millett Hybrid Owner's Manual CD, but since I'm the MOT for that, it would not be proper for me to give you a direct link to that.

 

[nyjets28]

thanks so much! unfortunately i can't get to it right now, but hopefully this will be the fix i need to get my amp to work. so every time i switch tubes, i will have to adjust the bias?