VHT Bias question

[Capulin Overdrive]

guess i should call VHT, but thought i'd put it out here also as a heads up.


when i was biasing up the D60 i allready had my Weber Bias rite out from doing the Elmwood so i used the bias rite on the D60. got it biased up right according to the Weber with the Chinese tubes.


then for shits and grins, checked it with a Multi-meter. it read way low according to the multi-meter method?


so guess my question is if using the multi-meter method is just for VHT tubes within a certain range or what?


really guess i trust the Weber over what the multi-meter was telling me, as it sounds great and seems pretty hot?

 

[RedB4Black]

Where is the bias pot? Is it labeled on the board. I haven't opened it up yet. I have a bias rite - I want to check the bias on mine.

 

[Capulin Overdrive]

Where is the bias pot? Is it labeled on the board. I haven't opened it up yet. I have a bias rite - I want to check the bias on mine.

the bias pot is pretty easy to find. also labeled really good to check with a multi-meter like VHT intended.


the hard part about biasing it, is transformer location and maybe size? one of the transformers is in the middle of the chassis, so makes it a little harder to do it upside down.


with the bias rite, i just left the chassis right side up and then tilted it up to get to the bias pot.


ended up really liking the Chinese power tubes in there!

 

[Greazygeo]

i've never used a bias rite. The Multi meter should give you the same readings....what PV do you have?

 

[Capulin Overdrive]

i've never used a bias rite. The Multi meter should give you the same readings....what PV do you have?

what's PV? power vavle?


the power tubes are i guess Shaugung out of my Elmwood? kt-88's. had them at 470volts and 54ma on the bias rite, the multi-meter said 1.05


got the chassis back in the headshell, but think the multi-meter should have read like 1.35?

 

[Greazygeo]

i've never used a bias rite. The Multi meter should give you the same readings....what PV do you have?

what's PV? power vavle?


the power tubes are i guess Shaugung out of my Elmwood? kt-88's. had them at 470volts and 54ma on the bias rite, the multi-meter said 1.05


got the chassis back in the headshell, but think the multi-meter should have read like 1.35?

Sorry its plate voltage...where are you taking our measurements from with the meter?

 

[Capulin Overdrive]

Sorry its plate voltage...where are you taking our measurements from with the meter?[/quote]



taking readings with the multi-meter where VHT says to, TP1 and TP2 i think?



just concerned if VHT's method works for all tubes or not? the VHT tubes are stickered 52, the Chinese 39, and the SED's i tried 47?

 

[Greazygeo]

Sorry its plate voltage...where are you taking our measurements from with the meter?

taking readings with the multi-meter where VHT says to, TP1 and TP2 i think?



just concerned if VHT's method works for all tubes or not? the VHT tubes are stickered 52, the Chinese 39, and the SED's i tried 47?[/quote]Those #'s on the tubes must be the tube matching info from whereever they were bought. If those #'s were way higher or lower from the stock tubes, the bias pot might not have enough range. Those are all pretty close, so you should be fine. I've not been in one yet to know what TP1 etc is....i just use pin 3 and the center tap of the OT method.

You have a D60 right? 54ma is about where i would set it.

 

[Capulin Overdrive]

Those #'s on the tubes must be the tube matching info from whereever they were bought. If those #'s were way higher or lower from the stock tubes, the bias pot might not have enough range. Those are all pretty close, so you should be fine. I've not been in one yet to know what TP1 etc is....i just use pin 3 and the center tap of the OT method.

You have a D60 right? 54ma is about where i would set it.[/quote]



yep, it's one of the newly voiced D60's.


how do you do the pin 3 and center tap? if you just had to lift the tube up a little, that would beat the shit out of having to pull the chassis?

edit; hell, just remembered you gotta pull the chassis to get at the bias pot anyways.


Weber's calculator said 52ma for 470 plate voltage = 70%, but i thought the 54ma sounded a little better.

 

[Greazygeo]

Those #'s on the tubes must be the tube matching info from whereever they were bought. If those #'s were way higher or lower from the stock tubes, the bias pot might not have enough range. Those are all pretty close, so you should be fine. I've not been in one yet to know what TP1 etc is....i just use pin 3 and the center tap of the OT method.

You have a D60 right? 54ma is about where i would set it.

yep, it's one of the newly voiced D60's.


how do you do the pin 3 and center tap? if you just had to lift the tube up a little, that would beat the shit out of having to pull the chassis?

edit; hell, just remembered you gotta pull the chassis to get at the bias pot anyways.


Weber's calculator said 52ma for 470 plate voltage = 70%, but i thought the 54ma sounded a little better.[/quote]Your Bias Rite should give you the same readings as my method. You still have to pull the chassis and put one of the probes directly on the tube socket pin three and the other on the center tap of the OT. The trick is being able to find that. If you don't feel comfortable working directly with the tube socket I'd just stick with the Bias Rite.

What is Weber's calc saying the KT88 puts out wattage wise? I usually go by 40 watts for current production stuff and bias at 60% not 70 or 75%. i like my tubes to run alittle on the cooler side so they don't get muddy towards teh end of the nite.

 

[Capulin Overdrive]

the Weber calculator doesn't say anything about watts as far as i know.


it has a pull down menu for tube type, then you put in a value for plate voltage, and it gives you a figure for the bias MA.


they've got charts for most tube types, but not the kt-88's.


i allways biased el-34's around 65-67%, but seem to being hotter with the 88's?