Tweet
Re: Tube question
I replaced my burned power tranny sunday afternoon, so I had to re-bias my amp. Let me tell you what I've been reading last week to come up to the correct bias point(conclussions)
6L6GC>6L6GB>6L6GA
OLD 5881=6L6GB
SOVTEK 5881WXT>6L6GB
(This is about power rating and plate B+ hadling)
In a forum post, I readed that someone set his 5881wxt amp runnig @ 500v B+ @ 65 mA for about a year without any noticeable issues. Did same last night & liked much @46 mA (less chunk, but more round/non harsh brite sound).
If you don't know how to measure currets openig up your amp, get a bias probe/metter, get a trim bias pot installed @ the rear panel and DIY! All you need to know is the B+ voltage of your amp(get measurred at tech-shop & label it) the max power dissipation of your desired tube and do this formula to get the bias current Bias mA=(Power D/B+ plate voltage)*0.7 up to 0.8*100. (0.7 to 0.8 is a factor that deppends of how hot you want you amp to run).
For example 6L6GC(30watts) @ 500v=(30/500)*0.8*100= 48 mA for a HOT amp.
Take the measure after heating the tubes, power on and NO SIGNAL= 0 vol & 0 Gain. Turn the trim pot til you get the desired mA current.
Matched means that each tube was tested untill found a pair or cuartet tha drains same plate current.
Why a matched cuartet? Because you are setting the same bias current for all of them (since you have 1 bias circuit and 1 bias pot). If you ask a tech to add independent bias circuit and bias pot for each tube, you can set bias current per-tube and need no more matched tubes.
With:
* EXTERNAL BIAS TRIM POT
* BIAS PROBE/METTER
* KNOW VALUES FOR B+ & TUBE POWER HANDLING
Every one should DIY. It's pretty easy and you can
* Re-tube
* Change tube type
* Find the bes bias setting
ALL BY YOURSELF!!
[ June 14, 2004, 08:26 AM: Message edited by: CZ V-KNIGHT ]
I replaced my burned power tranny sunday afternoon, so I had to re-bias my amp. Let me tell you what I've been reading last week to come up to the correct bias point(conclussions)
6L6GC>6L6GB>6L6GA
OLD 5881=6L6GB
SOVTEK 5881WXT>6L6GB
(This is about power rating and plate B+ hadling)
In a forum post, I readed that someone set his 5881wxt amp runnig @ 500v B+ @ 65 mA for about a year without any noticeable issues. Did same last night & liked much @46 mA (less chunk, but more round/non harsh brite sound).
If you don't know how to measure currets openig up your amp, get a bias probe/metter, get a trim bias pot installed @ the rear panel and DIY! All you need to know is the B+ voltage of your amp(get measurred at tech-shop & label it) the max power dissipation of your desired tube and do this formula to get the bias current Bias mA=(Power D/B+ plate voltage)*0.7 up to 0.8*100. (0.7 to 0.8 is a factor that deppends of how hot you want you amp to run).
For example 6L6GC(30watts) @ 500v=(30/500)*0.8*100= 48 mA for a HOT amp.
Take the measure after heating the tubes, power on and NO SIGNAL= 0 vol & 0 Gain. Turn the trim pot til you get the desired mA current.
Matched means that each tube was tested untill found a pair or cuartet tha drains same plate current.
Why a matched cuartet? Because you are setting the same bias current for all of them (since you have 1 bias circuit and 1 bias pot). If you ask a tech to add independent bias circuit and bias pot for each tube, you can set bias current per-tube and need no more matched tubes.
With:
* EXTERNAL BIAS TRIM POT
* BIAS PROBE/METTER
* KNOW VALUES FOR B+ & TUBE POWER HANDLING
Every one should DIY. It's pretty easy and you can
* Re-tube
* Change tube type
* Find the bes bias setting
ALL BY YOURSELF!!
[ June 14, 2004, 08:26 AM: Message edited by: CZ V-KNIGHT ]
Comment