Auto-bias board and a Weber WS1

Apologies if this seems like beating a dead horse, I wanted to get some insite into using a Weber WS1 with the Auto Bias board now available on the tubes4hifi site.

I am currently using a gz34 with the yellow sheet diode mod and haven't had any issues but would like to use a copper cap to avoid any future catastrophic rectifier failures if possible.

My understanding is with the auto-bias board the output tubes will slowly be introduced to the HV so the weber would not cause any issues under normal operation with the bias board. Is this correct?

Also I cannot find info if the yellow sheet diodes should be removed from the rectifier socket before using the weber. Any insite would be greatly appreciated. Thanks.

The yellow sheet diode mod simply puts a pair of UF4007 or 1N4007 before whichever rectifier you plug into the socket. I don’t think it would affect the auto-bias board but I could be wrong.

The only issue I heard with the WS1 is it comes up too fast when powering on, you can get them with a thermistor, not sure if that or the slow autobias power up helps the issue.

The diode mod, I thought that was there mainly so that if there was a power off/power on too quickly, it would stop the power tubes from sending current back to the tube rectifier, so it doesn't blow, the WS1 I think handles it OK, not sure if the AB has anything to do with that.

That all makes sense, I did get the thermistor with mine. Thanks for the info.

Maybe Roy, Pavel, or Bob could weigh in here. There's more than a little interest.
Thanks

New2Tubez wrote:Maybe Roy, Pavel, or Bob could weigh in here. There's more than a little interest.
Thanks

I was able to answer my own questions. I should have searched more previous postings before even posting a new thread.

https://dynacotubeaudio.forumotion.com/t3430-there-s-a-good-time-to-use-the-weber-ws-1-ss-rectifier?highlight=Weber

That thread has some good information and deserves a read from anyone interested in this topic.

Also the thread below specifically on page 3-4

https://dynacotubeaudio.forumotion.com/t2639p50-weber-wz68-now-not-recommended-on-weber-website?highlight=Weber+ws

Hmmmmm. In my case, wall ac comes in at between 119-122+ so my ST-120 is on the recommended 5A variac set to 117vac. That post mentions the opposite- low voltage.  

So will the WS1 w/thermistor be ok w/ yellow sheet diode mod and the new Auto Bias board w/mini fuses..?  I'm currently w/ 5AR4, no TD board, or AB board.

Most of this goes over my head but I'm trying to understand and do it right.  Thanks for your patience.

One question I am not able to answer, since the WS1 has no sag resistors it will increase B+ and will require the bias to be reset.

Is the bias level set on the A/B board potentiometer affected by this rise in B+ from the WS1?

I have not tried yet but I should be able to test by removing all tubes and testing bias points on the A/B board at various levels of incoming voltage with a variarc.

New2Tubez wrote:Hmmmmm. In my case, wall ac comes in at between 119-122+ so my ST-120 is on the recommended 5A variac set to 117vac. That post mentions the opposite- low voltage.  

So will the WS1 w/thermistor be ok w/ yellow sheet diode mod and the new Auto Bias board w/mini fuses..?  I'm currently w/ 5AR4, no TD board, or AB board.

Most of this goes over my head but I'm trying to understand and do it right.  Thanks for your patience.

I am going to test the bias board like stated in my previous post and will let you know my findings.

One part I should mention when you install your bias board and if your using the fuses, make sure your four cathode connections from the A/B board go to pin ONE on all 4 sockets. Then the fuse is used to bridge pin one to eight.

Thanks for your help!

I appreciate the tip on the fuse connections as well.

I tested the bias points on the A/B board at 123V my normal line voltage and at 114V. The bias reading from the board remained steady at .506 during both tests.

This would suggest the bias level set on the board is not affected by line voltage fluctuations and would not need to be reset after switching over to the WS1.

I will try mine and post results shortly. I think I am also going to rewire the bias test points to the resistors on the A/B board.

Kramer wrote:I tested the bias points on the A/B board at 123V my normal line voltage and at 114V. The bias reading from the board remained steady at .506 during both tests.

This would suggest the bias level set on the board is not affected by line voltage fluctuations and would not need to be reset after switching over to the WS1.

Makes sense. But maybe if the plate voltage were to go up, after installing the WS1, then if you were calculating bias setting based on the 70% theory, you may then have to readjust bias anyhow.

jfine wrote: Makes sense. But maybe if the plate voltage were to go up, after installing the WS1, then if you were calculating bias setting based on the 70% theory, you may then have to readjust bias anyhow.

That is correct, if the plate voltage increases and since the cathode current is used by the A/B board.

Does this seem correct?
The amp has around 485V on the plates. Replacing the gz34 with a WS1 whould add an additional 17V to the plates and 70% on a kt88 plate is 29.4watts.

29.4 / 502 = 0.058

So the bias by that calculation is up to 580mv.

But if you use that same formula above I believe Bob recommends biasing kt88s on a st120 at 500mv, so about 24 watts and 485 on the plates, which is about 57%.

So with using Bobs reduction down to about 57% that would be

23.94 / 502 = 0.0476

So to account for the additional voltage from the Weber I would set the bias on the A/B board to 476mv?

Would any one please let me know if this at all seems correct? I could really use a second set of eyes.

The math seems right,

I think it depends on what you want, longer tube life or trying to target a KT88 to sound its best? Actually I'm up a little higher than 70% on mine. The autobias should provide longer tube life anyways...

I'm wondering what the expectation of a KT120 tube is? I've been running mine almost daily for 3 1/2 years in M125s, I check the bias every month or so when I remember and its right on .500 every time. I do have rock solid AC voltage from TVA and step down to 118VAC running a Mullard GZ37 rectifier tube, no diode mods. I don't see any reason for me to mess with my amps.

10-E-C wrote:I'm wondering what the expectation of a KT120 tube is? I've been running mine almost daily for 3 1/2 years in M125s, I check the bias every month or so when I remember and its right on .500 every time. I do have rock solid AC voltage from TVA and step down to 118VAC running a Mullard GZ37 rectifier tube, no diode mods.  I don't see any reason for me to mess with my amps.

I am not sure what the plate voltage is of the M125's but running kt120's at .500 in a ST120 is running them at 35%. I would guess on/off cycles would add a little extra wear but I would say they will last a long time.

Jfine, thanks for looking. I am going to leave the bias where it's at and try the tubes biased a little higher with the Weber.

Why not just get a WX-68? They ramp up quicker than tubes but at least there's a delay, unlike the sudden in-rush from the WS-1.

WS1 doesn't have a sag resistor so it doesn't get nearly as hot, its available with a thermistor which I got and it works beautifully. I opened it up and can easily replace diodes but I doubt I ever will need to. Polished her up to a near mirror finish as a bonus, I think it looks great.

PLUULLLL_EZZZZZZ
do not power up tube equipment with no tubes in it unless you are using a variac set to a lower input voltage.
Any capacitors that normally see 500v could easily see 600v and blow up in your face !!!!!!!!!!!

Roy, thanks for the reply. I will not start the amp without tubes at regular line voltage again. Thanks for looking out for the guys still learning. I really appreciate this forum.

I do want to clarify at no time did I have the Weber WS1 installed and then powered up the amp. I removed all tubes as well as the WS1 before powering up and taking measurements.

Can someone clarify a couple of details regarding the AB board, time delay and using the WS1 vs a WZ68?

I'm having the AB board installed on my VTA 120. As I understand the threads on this topic (plus input from Ben, who is installing the board for me), if the AB board is installed there is no need to install the time delay board to protect the driver tubes if you plan on using a solid state rectifier like the WS1 or WZ68.

How much time delay does the AB board provide?

Is there a specific amount of time (or minimum) delay that is recommended?

How does the time delay board (or AB board) actually keep the onrush of current from the WS1 or WZ68 from reaching the tubes?

I also understand that if you use the WS1 you should ensure the line voltage doesn't exceed 120v. I have a variac but sometimes the line voltage floats during a listening session, hardly ever, but it does happen once in a while above 120v.

Is there is a possibility of damage to the amp if the line voltage raises above 120v for short periods of time if I'm using the WS1?

Besides a variac what else can you use to ensure line voltage stays below a specific level?

Does the WZ68 produce more current than the gz34 tube, and if so, why would there even be a debate about using it over the WS1 if they both accomplish the same goal (i.e., produce enough current to fully drive the output tubes under load?)

Thanks in advance for helping me out on this. I really want to use SS rectification but am not very confident I should until I understand the options more clearly.

Hi JSL,
surprised no response to this yet.   I was gone on vacation a few days.
Most of the answers to this are in the documentation, but let me summarize . . . .

How much time delay does the AB board provide? - red LEDs on for about 20 seconds before ANY bias is applied, then about 40 seconds until bias is ramped up to correct set level.

Is there a specific amount of time (or minimum) delay that is recommended?  not sure if you are asking about the auto-bias (preset) or the TDR board (also preset)

How does the time delay board (or AB board) actually keep the onrush of current from the WS1 or WZ68 from reaching the tubes? the output tubes will not conduct current until they have enough bias, about 1 minute

I also understand that if you use the WS1 you should ensure the line voltage doesn't exceed 120v.
I have a variac but sometimes the line voltage floats during a listening session, hardly ever, but it does happen once in a while above 120v.
The basic amp circuit was designed 60+ years ago, when line voltage was around 115v.  At 120vac line voltage the B+ is about 25v higher, and at 125vac about 50v higher than design spec.
 Using a WS1 or other solid-state rectifier will increase the B+ an additional 20-25vdc above even that amount !!   So keep input AC at 115vac or lower !!

Is there is a possibility of damage to the amp if the line voltage raises above 120v for short periods of time if I'm using the WS1?  Yes, possible.  Most likely damage to the quad cap, not to anything else.

Besides a variac what else can you use to ensure line voltage stays below a specific level?   Line conditioners with a REGULATOR are available but are very expensive

Does the WZ68 produce more current than the gz34 tube  most definitely, the GZ34 tube is rated at a MAX of 250ma, which exceeds the output current if tubes run at 55ma each.
I personally do NOT recommend using a tube rectifier with KT88 output tubes since they work best with current between 55-70ma each tube or 220-280ma total plus the 25ma needed to run the driver tubes.
A WZ68 is current rated at 450ma.  A WS1 is current rated at 1000ma (but it also has an additional 16-17v of output which is NOT needed!)

A bucking transformer can also be used to reduce wall voltage. Lots of info in this forum on how to build one.

Thanks for answering my questions. Regarding dkcumentation, as I do not yet have the board I don’t have the documentation. Everything else is clear—again thank you for taking the time to respond.