Welcome, Guest. Please login or register.
Did you miss your activation email?
December 23, 2024, 01:44:41 AM
Home Help Search Login Register
News: Ceriatone Forums are up and running!!!
 
Guests please register
Note: If you want to help you can donate to keep the forums alive.



Do you want to advertise on this forum ? Send me a private message.



Amplified Parts
+  Ceriatone Forum
|-+  Ceriatone
| |-+  Overtone
| | |-+  OTS 50 - bias problem/question
« previous next »
Pages: 1 [2] Go Down Print
Author Topic: OTS 50 - bias problem/question  (Read 17717 times)
GuitarHack
Jr. Member
**
Offline Offline

Posts: 57


View Profile
« Reply #15 on: May 26, 2013, 05:49:27 AM »

Did some more research and now I'm sure the problem is with V5.
With any tube in V5 and no tube in V4, I get no sound.

Seeing as how the bias current gets to the tube through that 1 ohm resistor and its open, the current's not getting there, even though I get a reading.

So, I'm wondering - can I bypass that 1 ohm resistor and see if that fixes the problem ?
V5 should then get sound even if V4 is pulled out ?

What I don't understand is - if that resistor is creating an open circuit, where are the mV on pins 1 & 8 coming from ?
Why don't pins 1 & 8 read zero mV ?
« Last Edit: May 26, 2013, 06:12:35 AM by GuitarHack » Logged

OTS 50
2004 PRS Single Cut Trem
Mollenhauer Strat
custom Paduk neck-through Strat
Mack Heatseeker 36
Peavey Classic 50
plasticvonaband
Hero Member
*****
Offline Offline

Gender: Male
Posts: 747


Pickin and Grinnin since 1989


View Profile WWW
« Reply #16 on: May 26, 2013, 11:04:18 AM »

The 1 ohm resistors provide a way to safely read the bias current with a DMM, and connect the cathode (pin Cool to ground. Instead of reading the actual current, your are reading the voltage drop across that resistor. Through the magic of electrical engineering and math that I barely grasp, the mV reading equals the current reading but is safer to measure. If V5's sensing resistor is bad it could cause a problem, as pin 8 and externally only pin 1 are the cathode and connected to ground. I would check the external connection between pin 8 and pin 1 along with changing that 1R 2W resistor, just to be safe.

Gregg
Logged

Overdrive is like peanut butter. Some like it crunchy, some like it creamy.
Bluesmaster 50 2x12 combo and some guitars.
GuitarHack
Jr. Member
**
Offline Offline

Posts: 57


View Profile
« Reply #17 on: May 26, 2013, 05:11:09 PM »

THanks Gregg,
I (sort of) understand what the 1 ohm resistor is for - converting mA to mV so you can easily measure the bias.
What I'm wondering is if I can bypass that resistor with a piece of straight wire to see if that gets V5 working again.
I know I can't measure that side in that case.

I want to see if the problem is just the resistor, or there's something else going on upstream from there.

Pins 8 & 1 are connected together and are getting voltage - the same reading as at the bias lug.  around 35 mV.
And it changes as I adjust the bias pot. I don't understand how that's possible if the resistor is not passing any current.

Or is it just that pins 1 & 8 are not grounded ? Could that be why V5 is not firing up ?
« Last Edit: May 26, 2013, 05:51:19 PM by GuitarHack » Logged

OTS 50
2004 PRS Single Cut Trem
Mollenhauer Strat
custom Paduk neck-through Strat
Mack Heatseeker 36
Peavey Classic 50
plasticvonaband
Hero Member
*****
Offline Offline

Gender: Male
Posts: 747


Pickin and Grinnin since 1989


View Profile WWW
« Reply #18 on: May 26, 2013, 07:08:44 PM »

If it wasn't grounded, you would be getting zero current flow across. What kind of voltage are you getting at the plates (pin 3)? Also you said you unplug and plug your c-lator with the amp powered on? Is it on or off standby? Generally you shouldn't connect/disconnect that unless the amp is powered down or at least in standby. Also, when you do your testing are all your levels turned down?

Gregg
Logged

Overdrive is like peanut butter. Some like it crunchy, some like it creamy.
Bluesmaster 50 2x12 combo and some guitars.
GuitarHack
Jr. Member
**
Offline Offline

Posts: 57


View Profile
« Reply #19 on: May 27, 2013, 12:23:02 AM »

If it wasn't grounded, you would be getting zero current flow across. What kind of voltage are you getting at the plates (pin 3)? Also you said you unplug and plug your c-lator with the amp powered on? Is it on or off standby? Generally you shouldn't connect/disconnect that unless the amp is powered down or at least in standby. Also, when you do your testing are all your levels turned down?

Gregg
I'm getting 469 V on pin 3. Master Volume is turned off.

Unplugging the C-lator with the amp on is ok if the volume is low. Its never been a problem - I don't think connecting/disconnecting it can harm the amp.  Maybe blow a speaker if the volume is up.
Logged

OTS 50
2004 PRS Single Cut Trem
Mollenhauer Strat
custom Paduk neck-through Strat
Mack Heatseeker 36
Peavey Classic 50
GuitarHack
Jr. Member
**
Offline Offline

Posts: 57


View Profile
« Reply #20 on: May 27, 2013, 06:33:35 AM »

What I need to know, if you can tell me, is if I can safely bypass that 1 ohm resistor just to see if that 'fixes' the problem.
If so, I can replace the resistor myself.
If its not safe to bypass, or if the bypass doesn't fix the problem, then I'll probably have to take it to a tech, which I can't really afford right now.
Logged

OTS 50
2004 PRS Single Cut Trem
Mollenhauer Strat
custom Paduk neck-through Strat
Mack Heatseeker 36
Peavey Classic 50
plasticvonaband
Hero Member
*****
Offline Offline

Gender: Male
Posts: 747


Pickin and Grinnin since 1989


View Profile WWW
« Reply #21 on: May 27, 2013, 07:01:50 AM »

Yup, you can run the cathode straight to ground, just can't test the bias on that one without some different equipment, but you can bypass it.

Gregg
Logged

Overdrive is like peanut butter. Some like it crunchy, some like it creamy.
Bluesmaster 50 2x12 combo and some guitars.
GuitarHack
Jr. Member
**
Offline Offline

Posts: 57


View Profile
« Reply #22 on: May 27, 2013, 07:21:55 AM »

Yup, you can run the cathode straight to ground, just can't test the bias on that one without some different equipment, but you can bypass it.

Gregg
Muchos Gracias, Gregg. I'll give that a try.
Logged

OTS 50
2004 PRS Single Cut Trem
Mollenhauer Strat
custom Paduk neck-through Strat
Mack Heatseeker 36
Peavey Classic 50
GuitarHack
Jr. Member
**
Offline Offline

Posts: 57


View Profile
« Reply #23 on: May 27, 2013, 08:00:49 PM »

Bypassed the 1 ohm resistor and all is well.  Going to get a replacement now.
Thanks Gregg.  You saved me a small bundle.
Cheers,
Jon
Logged

OTS 50
2004 PRS Single Cut Trem
Mollenhauer Strat
custom Paduk neck-through Strat
Mack Heatseeker 36
Peavey Classic 50
plasticvonaband
Hero Member
*****
Offline Offline

Gender: Male
Posts: 747


Pickin and Grinnin since 1989


View Profile WWW
« Reply #24 on: May 27, 2013, 08:29:22 PM »

You're welcome. Sometimes it IS the simplest problem and fix! Smiley

Gregg
Logged

Overdrive is like peanut butter. Some like it crunchy, some like it creamy.
Bluesmaster 50 2x12 combo and some guitars.
GuitarHack
Jr. Member
**
Offline Offline

Posts: 57


View Profile
« Reply #25 on: May 28, 2013, 12:25:12 AM »

Hopefully, it won't happen again.  Its unusual for a resistor to just quit with no sign of burn, isn't it ?

Anyway, another question - really for Pickmaster, but since we're already talking and you may know the answer....

While at the electronics store I bought some extra 100K and 68K resistors to try Pickmaster's slope resistor mod.
I couldn't find any brown ones like the one that's in there, so I just got plain carbon fibre, 2 Watters.
I believe the slope resistor is 3W.  I don't know if the brown ones are carbon fibre or what.

Can I put that 2 Watt resistor in there ?
Logged

OTS 50
2004 PRS Single Cut Trem
Mollenhauer Strat
custom Paduk neck-through Strat
Mack Heatseeker 36
Peavey Classic 50
plasticvonaband
Hero Member
*****
Offline Offline

Gender: Male
Posts: 747


Pickin and Grinnin since 1989


View Profile WWW
« Reply #26 on: May 28, 2013, 02:25:22 AM »

I *think* 2 watts is fine from what i recall being told on here before, and that's what i got when i was planning to change the resistor out, because mouser was out of non-bulk 3 watters a the time. I picked up metal film ones from mouser just to be on the safe side

http://www.mouser.com/ProductDetail/Vishay-BC-Components/PR02000206802JR500/?qs=sGAEpiMZZMtlubZbdhIBIDqBBcd6vlUvTCvt5QvopJA%3d
$0.10 USD each, no minimum

They have the 3 watters in stock right now as well

http://www.mouser.com/ProductDetail/Vishay-BC-Components/PR03000206802JAC00/?qs=sGAEpiMZZMtlubZbdhIBIHDatFdBRARu3kAymlOBwNM%3d
 $0.46 USD each, no minimum
Logged

Overdrive is like peanut butter. Some like it crunchy, some like it creamy.
Bluesmaster 50 2x12 combo and some guitars.
GuitarHack
Jr. Member
**
Offline Offline

Posts: 57


View Profile
« Reply #27 on: May 28, 2013, 04:58:38 PM »

I wonder if something was wonky from day 1.   After replacing the 1 ohm resistor and putting back the pair of JJ's I've been using for the last year, the bias measurement was a lot closer from tube to tube.

Anyway, I did the slope resistor mod - with a temporary internal switch from 100K to 68K.  Been playing with the 68K and loving it!  Still have to see how it sounds at gig level, but sounding rather stellar at home.
I'm also running the bias a bit cooler than before.  Found a bias calculator online - and now that I know the voltage on the pins, I can bias more accurately.  Apparently, the higher the voltage, the lower the bias setting to get the same dissipation.

The amp is starting to sound like what I bought it for.   Can't wait to gig with it this weekend.

Thanks again to  plasticvonaband, Pickmaster and others who've been so generous with their knowledge and skill.
Logged

OTS 50
2004 PRS Single Cut Trem
Mollenhauer Strat
custom Paduk neck-through Strat
Mack Heatseeker 36
Peavey Classic 50
Pages: 1 [2] Go Up Print 
« previous next »
Jump to:  


Login with username, password and session length

Powered by MySQL Powered by PHP Powered by SMF 1.1.12 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!

CeriaTone Forum is not afiliated with Ceriatone Amplifications. The CeriaTone and name, logo and related trademarks and service marks, owned by CeriaTone. , are registered and/or used in the U.S. and many foreign countries. All other trademarks, service marks, and trade names referenced in this site are the property of their respective owners.