Best New EL34's for 8b

[Perkinsman]

Anyone have particularly good experiences with new mfr'd tubes in their 8b? Also, do I still have to get a matched quartet since the 8b allows you to bias individually?

 

[Chrisxo55441]

No you do not need matched EL34's. I do keep mine the same manufacture and same getters though. ive never tried but i think you can probably mix them if you like to try different things. i have not tried any new manufactured either so dont know about them. RFT (Siemens) are close to Mullards sound wise to me and are about half the price still not cheap but reasonable i think.

 

[jstang]

I like the Mullard re-issues in the 8b I had and currently in my 9s.

 

[Perkinsman]

I'll hunt for those RFT tubes, they sound interesting. I've never biased this amp. Is it done with the knob and meter or do I need to open the chassis?

 

[Pio1980]

Many like the ElectroHarmonix 6CA7 matched pairs.
Biasing is done to the line on the meter on each tube from the pots on top of the chassis powered up after warmup. I recommend downloading the owner manual.
NEVER EVER CHECK BIAS WITH THE AMP PLAYING, EVER!! You risk ruining the totally unobtanium meter.

 

[Perkinsman]

Many like the ElectroHarmonix 6CA7 matched pairs.
Biasing is done to the line on the meter on each tube from the pots on top of the chassis powered up after warmup. I recommend downloading the owner manual.
NEVER EVER CHECK BIAS WITH THE AMP PLAYING, EVER!! You risk ruining the totally unobtanium meter.

Roger that. I am able to adjust 3 of the bias pots but the 4th doesn't move the needle on the meter. Is there a component I can check under the hood?

 

[Pio1980]

Roger that. I am able to adjust 3 of the bias pots but the 4th doesn't move the needle on the meter. Is there a component I can check under the hood?

Yes, there are components associated with the bias pots that can be checked. Is it high or low on the bias?

 

[Perkinsman]

The needle works fine on 3 of the tubes but doesn't move on one of the tubes, stays on the far left position. I switched tubes in that position and the needle still is motionless. What components do I want to check?

 

[Pio1980]

The needle works fine on 3 of the tubes but doesn't move on one of the tubes, stays on the far left position. I switched tubes in that position and the needle still is motionless. What components do I want to check?

Which tube position?
We may start with pulling the output tubes and carefully checking the socket voltages to chassis of the nonbiasing tube position against another position. We are primarily interested in tube pin positions 3, 4, and 5. They are numbered clockwise from the bottom, starting at the index notch, counterclockwise from topside. Pins positions 3 and 4 may be at potentially dangerous high voltage levels near 500 VDC, so exercise extreme caution.

 

[Perkinsman]

Which tube position?
We may start with pulling the output tubes and carefully checking the socket voltages to chassis of the nonbiasing tube position against another position. We are primarily interested in tube pin positions 3, 4, and 5. They are numbered clockwise from the bottom, starting at the index notch, counterclockwise from topside. Pins positions 3 and 4 may be at potentially dangerous high voltage levels near 500 VDC, so exercise extreme caution.

 

[Perkinsman]

It's B2...pin 3 438vdc,pin 4 312vdc,pin 5 -38.25

 

[Pio1980]

It's B2...pin 3 438vdc,pin 4 312vdc,pin 5 -38.25

Is this from bottom with tubes installed?

 

[Pio1980]

If it sound basically ok thru both channels at reasonable loudness, I suspect problem with bias switch in the problem position.

 

[Pio1980]

If so, a provisional fix may be to set bias at problem socket by matching pin 3 voltage with opposite tube in that channel.
Inconvenient, yes.
Inspect switch to see if there is a problem with contacts in that test position to meter.

 

[Perkinsman]

If so, a provisional fix may be to set bias at problem socket by matching pin 3 voltage with opposite tube in that channel.
Inconvenient, yes.
Inspect switch to see if there is a problem with contacts in that test position to meter.

I assume B1 would be the same channel, pin 3 444 pin 4 445 pin 5 -40
(B2 was......438..........312.........-38.25)
Pin 4 has a 133v difference. Would the screen grid cause the issue?

 

[crooner]

Check the 100 ohm screen resistor on that particular tube socket. Often these open or change value and you won't be able to bias that output tube. Replace with same type (Carbon) and 1/2 watt rating. 5% tolerance is better.

As for new tube recommendations, the SED/Winged "C" (now NOS) are excellent. The New Sensor Svetlanas are not too shabby either, and cheap. I recently acquired another 8B and it had these installed. Sounds great to me..

 

[Perkinsman]

Check the 100 ohm screen resistor on that particular tube socket. Often these open or change value and you won't be able to bias that output tube. Replace with same type (Carbon) and 1/2 watt rating. 5% tolerance is better.

As for new tube recommendations, the SED/Winged "C" (now NOS) are excellent. The New Sensor Svetlanas are not too shabby either, and cheap. I recently acquired another 8B and it had these installed. Sounds great to me..

I'll replace that resistor tomorrow. Do you think that it would resolve both the bias dial issue and the lower screen voltage than B1? You're the 2nd person to mention Winged C tubes this week...are they really audibly that much better than a $30 EH quartet?

 

[Pio1980]

The screen stopper resistor could definitely cause the broad differential to 3. It should otherwise be within a few volts at least. Use 100 Ohm 1/4 Watt replacements as fail-safes to protect the OPT from flashover overloading.

 

[crooner]

I always use 1/2 watt, but Pio1980 is right that a 1/4 watt will provide more protection. I do always find the 100 ohm 1/2 watt screen resistors toasty or overheated on Marantz tube amps.

In regards to the SED's, I just happen to use them during their heyday and liked the sound. I also used the Gold Lion KT77 reissue, and liked it, although they were a tad dark, more of a 6L6GC beam tetrode sound.

I am curious about the EH's myself. I may try a quad sometime soon!

 

[Perkinsman]

I always use 1/2 watt, but Pio1980 is right that a 1/4 watt will provide more protection. I do always find the 100 ohm 1/2 watt screen resistors toasty or overheated on Marantz tube amps.

In regards to the SED's, I just happen to use them during their heyday and liked the sound. I also used the Gold Lion KT77 reissue, and liked it, although they were a tad dark, more of a 6L6GC beam tetrode sound.

I am curious about the EH's myself. I may try a quad sometime soon!