Champ Went dead with 16 Ohm Ext Speaker

L

Liquidfusion

Groupie
Messages
23
1965 Fender Blackface Champ - Modded by Gerald Weber Kendrick Amps

Read wrongly - it was "possible to use a 16 ohm Speaker with a 4 ohm Amp"
Detached the internal 4 ohm Kendrick speaker and added a 16 ohm external Alnico Blue Speaker
After 5 min the amp went dead. red light out. Slight burning smell

Took amp apart. Rectifier Tube =J J GZ 34.
Power Tube : Tung Sol 6550.
Preamp : ECC83 tube
Tested tubes with a Precision Tube Tester + Continuity Test using a Fluke 101 MM

6550 was NG - all other tube OK

Replaced rectifier tube with original 5Y3 tube
Replaced Power Tube with 6V6 GT Raytheon tube
Kept ECC83 preamp tube
Replaced 1 Amp 250V Fuse - Continuity Test = ok Beep
Ame turned on - Red Light - Sweeter sound !!
______________________________________________________________________

Not original transformer - More powerful OT - installed for me by Gerald Weber

Is it safe to put the GZ34 rectifier back in? Why is that tube there?
Is it safe to put a new 6550 Tube in? - have replacements
Pro guitar friend said get the transformer checked - is this needed now?

Small burn area on chassis under the 6550 tube - only damage in the amp - along with the 1 Amp fuse
No burned wires. Circuits look fine

Learned the hard way - do not mismatch ohms with speaker in tube amps!!!
Thank for comments / advice - insights
 

Attachments

  • PXL_20240315_011823992.jpg
    PXL_20240315_011823992.jpg
    137.9 KB · Views: 13
  • PXL_20240314_220410322.jpg
    PXL_20240314_220410322.jpg
    118 KB · Views: 8
  • PXL_20240314_214321208.jpg
    PXL_20240314_214321208.jpg
    1.8 MB · Views: 10
  • PXL_20240314_214223931.jpg
    PXL_20240314_214223931.jpg
    1.2 MB · Views: 9
  • PXL_20240314_214214624.jpg
    PXL_20240314_214214624.jpg
    1.7 MB · Views: 10
  • PXL_20240314_214150843.jpg
    PXL_20240314_214150843.jpg
    2.6 MB · Views: 10
  • PXL_20240315_013020330.jpg
    PXL_20240315_013020330.jpg
    134.7 KB · Views: 10
  • PXL_20240315_012945424.jpg
    PXL_20240315_012945424.jpg
    149.8 KB · Views: 9
  • PXL_20240315_011957386.jpg
    PXL_20240315_011957386.jpg
    149.9 KB · Views: 9
  • PXL_20240315_011914906.jpg
    PXL_20240315_011914906.jpg
    142.6 KB · Views: 15
Oh my, good to hear that it turned back on after all. 🙂

And yeah, cabs can be mismatched both ways. When the cab impedance is bigger than what the amp wants to see, one step is usually safe, e.g. 8 ohms output into 16 ohms cab.

But 4 ohms amp into 16 ohms cab -> amp goes brrrrrrr
 
Liquidfusion said:
Detached the internal 4 ohm Kendrick speaker and added a 16 ohm external Alnico Blue Speaker
After 5 min the amp went dead. red light out. Slight burning smell
Click to expand...
Your output transformer is almost certainly fried. Tube amps cannot be safely driven into a higher impedance. Nor should they be driven into a lower impedance, but they are far more likely to survive that than the other way around. Unplugging the load is the same as infinite impedance, a dead short is the same as zero impedance.
 
Liquidfusion said:
Is it safe to put the GZ34 rectifier back in? Why is that tube there?
Is it safe to put a new 6550 Tube in? - have replacements
Pro guitar friend said get the transformer checked - is this needed now?
Click to expand...
The amp will not operate without the rectifier. The rectifier is the thing that takes the AC output of the power transformer and converts it to DC power to run the amp.

A GZ34 is the same as a 5AR4, a much more powerful tube than the original 5Y3. If the amp was functioning fine before you blew it up, then there no reason to suspect that the 5AR4 caused any problems.
 
Turned the amp - OFF - then detached the internal 4 ohm Kendrick speaker and added a 16 ohm external Alnico Blue Speaker

Replaced the fried 6550 tube and blown fuse

The amp is working now
 
NICE TO KNOW NOW

Z-Matcher 100w Impedance Matcher – Weber Speakers

www.tedweber.com www.tedweber.com
Here are the straight facts on impedance mismatches, and hopefully it will explain why there are contradictory reports:

ON A TUBE AMP
It is okay to run a LOWER impedance cabinet or speaker than the amp’s output impedance. Usually a mismatch of 2:1 is okay. (i.e. amp at 16 ohms, cab at 8 ohms.) It is dangerous to run a HIGHER impedance cabinet or speaker, as there is a potential for flyback currents that could either cause a catastrophic failure, or the stress over time can cause long-term failure eventually. (although with a tube amp, it’s really best that you keep the impedance matched.) Amp power is not affected by mismatching.

ON A SOLID STATE AMP
It is okay to run a HIGHER impedance cabinet or speaker than the amp’s output impedance. (i.e. amp at 4 ohms, cab at 8 ohms.) It is dangerous to run a LOWER impedance cabinet or speaker. Amp power output is reduced, the higher the impedance.

Bottom line: match it.
 
Liquidfusion said:
1965 Fender Blackface Champ - Modded by Gerald Weber Kendrick Amps

Read wrongly - it was "possible to use a 16 ohm Speaker with a 4 ohm Amp"
Detached the internal 4 ohm Kendrick speaker and added a 16 ohm external Alnico Blue Speaker
After 5 min the amp went dead. red light out. Slight burning smell

Took amp apart. Rectifier Tube =J J GZ 34.
Power Tube : Tung Sol 6550.
Preamp : ECC83 tube
Tested tubes with a Precision Tube Tester + Continuity Test using a Fluke 101 MM

6550 was NG - all other tube OK

Replaced rectifier tube with original 5Y3 tube
Replaced Power Tube with 6V6 GT Raytheon tube
Kept ECC83 preamp tube
Replaced 1 Amp 250V Fuse - Continuity Test = ok Beep
Ame turned on - Red Light - Sweeter sound !!
______________________________________________________________________

Not original transformer - More powerful OT - installed for me by Gerald Weber

Is it safe to put the GZ34 rectifier back in? Why is that tube there?
Is it safe to put a new 6550 Tube in? - have replacements
Pro guitar friend said get the transformer checked - is this needed now?

Small burn area on chassis under the 6550 tube - only damage in the amp - along with the 1 Amp fuse
No burned wires. Circuits look fine

Learned the hard way - do not mismatch ohms with speaker in tube amps!!!
Thank for comments / advice - insights
Click to expand...
I don't know the answer to your problems, but your trouble shooting approach is a bit baffling to me:

You had the amp modded to run a 6550 power tube and a higher power output transformer. This required a rectifier tube capable of delivering sufficient power for the now more muscular amp. You then...caused the amp to stop working because of mismatched speaker impedance. You checked the tubes and noted the power tube was fried, but all others were fine. Fuse was blown so you replaced it. Its possible that the fuse and powertube blowing saved the output transformer.

You then -- for whatever reason decided to go back to the stock rectifier and power amp tubes? Not sure why you made that choice? THe amp worked...so maybe the output transformer was saved by the fuse and power tube blowing up.

At this point, my next step would be to type into google "how to test if an output transformer is blown" or something similar. Assuming the hits were fairly mundane passive measurements with a multimeter, I'd do that. If the output transfomer seems fine based on those tests I would replaced BOTH the recitifier tube and power tube to the proper spec GZ34 and 6550 tubes.
 
Talked with Gerald Weber / Texas - I arced the socket - look at pins 3-4-5 - Socket needs to be replaced
 

Attachments

  • PXL_20240315_011957386.jpg
    PXL_20240315_011957386.jpg
    149.9 KB · Views: 14
Boudoir Guitar said:
At this point, my next step would be to type into google "how to test if an output transformer is blown" or something similar. Assuming the hits were fairly mundane passive measurements with a multimeter, I'd do that. If the output transfomer seems fine based on those tests I would replaced BOTH the recitifier tube and power tube to the proper spec GZ34 and 6550 tubes.
Click to expand...
I was cautious going back to the 5Y3 and the 6V6 tubes - lower current.

Right now the socket need to be replaced - arced pins 3-4-5 - can play the amp

After changing to a new socket, might try the GZ34 (seems fine) and a new 6550 (have replacement tubes)

Thanks!!
 

How to replace bad tube sockets Check Bias Fender Silver Face Champ Class A 6V6 tube guitar amp​



From the comments - use Belton, Micalex Sockets
 
Hi Amp is alive and doing fine after changing POWER Tube and fuse!

Before impedance mismatch -
Rectifier = GZ34 + Power Tube = 6550

New Tubes
Rectifier = 5Y3 and Power Tube = 6V6
 
You must log in or register to reply here.

Similar threads

L
Modding an Original Amp + Tubes
Replies
2
Views
397
Byrdman
Byrdman
Back
Top