very noisy Bassman 165AB

[pbman1953]

My friend's Bassman is real noisy. With nothing plued in it's very hissy and if you turn up eieht side it squeals

The pre amp tubes been swapped out and there's a new set of Winged C- 6l6's. The amp made noises even before the tube checking. It has power but it seemd to crap out too early. The volume control is all or nothing on both sides. Meaning not a gradual volume increase


Any ideas?

[sluckey]

It's a two channel amp. Do both channels behave the same? Give us some history. Is it an original 165, or a clone, or a brand new homebrew that has never played right?

[plexi50]

More info: Have all the PS caps been changed? If not and are old i would change them before powering up the amp any more

You dont want to cook your PT

[pbman1953]

Real Fender Silver Face Bassman

I looked under the cover and there are all Sprague Atom's-


2- 80 UF at 450V
3-  20UF at 500v

1- 16UF at 475V

Both channels act the same

[plexi50]

Can you show some pics of the caps and board?

[pbman1953]

I can't get the pic to 256kb

where can i send it?

[67polara]

Is that first cap on the left in backwards?  Seems like it to me.

Tony

[chocopower]

is in series with the second one.
That´s ok.

I had similar problems with Silverface fenders using "chocolate drop" caps in the Phase I.

A said, a pic of the board will be great.

[pbman1953]

I'm trying , how do you reduce the KB size of the picture. the system keeps rejecting

Thanks

[jim]

Use a photo editing program to crop and reduce resolution. I use Irfanview.


http://www.irfanview.com/

[pbman1953]

Great program!!  Thanks

[plexi50]

I'm trying , how do you reduce the KB size of the picture. the system keeps rejecting

Thanks

Try this. It works great for resizing. Just hope it is still as good as the version i have
http://www.freeimageconverter.com/downloads.aspx

What is the value of your grid resistors on the power tubes? It looks like 15K to my eyes. Should be 1.5K

[67polara]

It looks like 15K to me also.

Tony

[pbman1953]

Looks like the colors should be brown green red , not brown green orange. Is the the result of my issue from the wrong resistor value?

[pbman1953]

After checking you're both right. The wrong value has be installed. Are there any others that stand out?
Would I have to rebias after the proper ones were set in?


Thanks

[pbman1953]

Also you can see that many of the old caps have been replaced with new ones. Should there be any attention paid to the carbon comp caps? The older larger volatge ones have been replaced but not the smaller voltage ones

There are 2 almost heart shaped brown caps, one is a 250 @500 and other says 1000 @ 500

[plexi50]

The best thing for you to do to get started is to get the AB165 layout. Not the schematic. The layout will be easier for you to learn and understand. Just start at the first preamp tube and check each value against the layout. Follow the wire of each tube pin to the part that is in place on the layout and check it against yours. You will need to rebias and i bet the resistor on the bias trimmer pot has been changed to another odd value to make the biasing possable with those 15k grid resistors. If so change the resistor with the lead soldered to the top of the bias trimmer pot to the correct value usually 15K

Straighten up that brown coupling cap laying to the right. I may be touching other resistors there it shouldnt

The layout is fairly fuzzy and hard to make out the values but the schematic is very clear so which ever one you choose to use will be fine to get your amp working right  

[pbman1953]

Funny enough I measured the bias resistor on top of the control and it is a 15k. I guess the blue body is confusing the colored ring apperance.

[pbman1953]

mid section

[pbman1953]

right section

[plexi50]

Funny enough I measured the bias resistor on top of the control and it is a 15k. I guess the blue body is confusing the colored ring apperance.

Lift one end of that resistor on the bias pot and read it again to be sure your not reading a part of the pots 10K value
The new or i call it weird color coding for resistors sucks. Makes it that much harder to build or diagnose if your not familiar with the changes THEY made. Who is THEY anyway?

[pbman1953]

No, there is no wire there. Thew flash must of brought out a reflecion on the board

Question on replacing the screen resistors, I looked in my parts box and I have resistors that would total 1.68k instead of 1.5. Is that usable or does it have to be exact?

[pbman1953]

Removed the resistor on the bias pot and is dead on at 15k with a meter

[plexi50]

1.5K + is fine. It might be safer though if you just get (2) 1.5K resistors. A bunch of things tied around the power tubes isnt safe IMO

There a lot of voltage on pins 3 and you dont want  anything arching over onto anything to close those pins

Not to say it will happen but it makes for a cleaner job and less to go wrong

[pbman1953]

I have a 1k and .680k resistor for each tube. I can easily shrink tube the joint so nothing would arc

I agree with the neatness but I don't have time to get the resistors locally. I know I could mail order

Do you feel the correct value will solve the noisy problem and the volume issue? The volume issue was that the volume was quick to escalate instead of a gradual escalation. The correct type pot has be verified

Thanks

[pbman1953]

All set, 1.687k installed , rebiased the 6L6's at around 60% plate dissipation.


A HUGE thanks to everyone's help!!!


Rich

[plexi50]

Noise issues come from many sources. Grounding,Preamp tubes,Power tubes,Bad plate resistors,Bad input jack grounding etc:

Is it working and quiet now?

[pbman1953]

Hiss is gone

[plexi50]

Your bias was probably wacked and out of the range it should have been in
Glad it is working, Any other issues?

[pbman1953]

I use a Bias Rite that i bought from Weber VST. It wasn't that far off, a slight counterclockwise turn, from topside access.

Also I'm told the Bassman is rated at 4 ohms. Will it cut in half at 8?

What is the max load with 2 cabs?

When i got this peice it has a Webber Copper cap- WFW-Z34. I was told to remove it and go back to stock. Any thoughts on that?

I use 2 copper caps in my Sunn 2000s and they are excellent

Thanks

[plexi50]

Can i see a pic of your Bassman AB165 with a rectifier socket? Just curious. Some one else here may have a better knowledge of the 4 ohm impedance and the max load of dual cabs

[sluckey]

The WFW is not a plug-in recto, it's hardwired. The stock diodes are fine. And much cheaper than the WFW. I don't see any compelling reason to put it back stock though, unless you just want a stock AB165.

The WFW emulates the sag of an EZ34, which may be good for a guitar, but a bass would probably prefer the stiffer plain diodes.

[plexi50]

Ah ok!

[pbman1953]

This one doesn't have a rectifier socket. the last tech disconnected the diodes and installed the weber device

[pbman1953]

On a side note-


I see from this website- that my AB165 bias pot is a balance type. Does that mean that I would try to get both tubes as close to each other as possible for the bias adjustment?

http://www.ampwares.com/amp.asp?id=28


Also, does this mean that my amp is more of a black face than silver?


Thanks

[plexi50]

Look at pic and make these changes. Yes you are almost Blackface now as is the bias. Make the changes in the pic and you are done. Not much to changing the Silverface Fender amps to Blackface specs

I think whoever did the work on your amp just miss read some of the values. That 47K PI tail resistor should have been 100 ohm but SRV they say used a 47 ohm. 47 ohm not 47k.  100 or 47 ohm not critical but should be one of the two

[pbman1953]

1) On the resolder- tough pic to show solder quality, but it's solid

2) Will change the 47k to a 100 ohm

3) That wire is to ground.  

4) What is to be done with the 820 ohm resistor, anything?

5) all brown caps are now standing at attention

[plexi50]

Thats it. The 820 ohm feedback resistor is what you want so if it is already there your good to go /

[pbman1953]

Ok, one last one. Do I need to re-bias after the install of the 100 ohm resistor


Thanks for all your help!!!

[plexi50]

No rebiasing needed after installing 100 ohm presence resistor.  This is the long tail end of the PI which dictates your presence (Shine) thingamajiggy

[pbman1953]

ok, last one I promise.

First off I saved your website, very cool


Since this is a balance pot bias system. I guess I have to get the 2 tubes as close as possible to each other within 60-70% of plate disipation?

Thanks

[plexi50]

We all strive for perfection. But there is really no such thing. Look at the weber bias calculator online. You can enter your power tube plate voltage and get a ballpark of what you looking for in ma. Unless you have a 1 ohm resistor on pin 8 of each power tube to ground you wont be able to read ma. But you can get close enough by reading the voltage off pin 5 and get the -VDC of the grid

It says what that voltage is on most Fender schematics. For super duper accuracy you would need those 1 ohm cathode pin 8 resistors to groung and read the -MA from the pin side of the 1 ohm resistor

And if your real lucky and have a decent set of power tubes that are fairly well matched you may get close to an exact match in ma for your particular plate voltage

43-46 -VDC for your Bassman is the norm. 43 a little cold. 46-48 on the hot side

When i have a hard time biasing an amp according to a bias chart and the plate voltage changes up or down (There suppose to) i just kill the lights and in the dark listen to the amp as i turn the bias pot and listen for an increase in loudness from the speaker. Then i purposely try and make the tubes redplate just for a second and then back the bias off until the redline has just faded away

Thats the actual working load (current draw) and condition that the amp wants to see. Dont have to do this all the time but it depends on how many matched tubes you happen to have. I have 3 set's of RCA Blackplate 6L6GC tubes and not one pair is a perfect match. If i wind up with -43 on one and -48 on the other than thats life using old tubes. Thats the gamble i take every time i buy off Ebay. There is a slight difference in each tubes output at this point but not enough to matter or even hear the difference

There is no audible output loss in a 4 ma difference. It's all an illusion

[Willabe]

FWIW, plexi's been around the block a time or two, I'd go with/try what he's sayin.


       Brad          

[plexi50]

Im a newbie.