Help Needed: Retubing Ibanez TSA30 amp and biasing

[ibarakishi]

I have a Ibanez TSA30 Combo amp that is starting to make sounds that make me guess that it is time to change the stock tubes out for new ones. I have loved playing this amp a lot. I have never changed tubes out by myself before, or biased an amp, but have started to read as much as i can online about it. And everyone i know usually just takes it to a tech to be changed and biased. I believe that my amp needs to be biased if i am not mistaken. I thought i would post this here and ask about some things and see if anyone had any experience with this to share some information from experience. I don't live close to anyone who can really help me with this stuff, and have been wanting to learn about doing things like this for a while now. This year i am trying to learn more about being able to maintenance and do various repairs/upgrades on my gear (with amps, pickups, etc.). I would like to share this information with others here and possibly help people that are interested in these things once i can slowly gain this experience myself. So thank you in advance for any help or sharing thoughts. I really appreciate it and will try to share this will other people that are interested as well.

For the biasing, i know that i will need 1.) a multimeter and 2.) a bias probe. Eurotubes makes a bias probe that is pretty cheap to connect into a multimeter available for order online, but i didn't know what the cheapest options were for ordering a multimeter. Any suggestions? Is there anything that i should stay away from? Also with the Biasing, i am unclear about how to figure out what the numbers should read for the bias. If somebody understands this well, i would be thankful for someone to explain it to me a little bit more.

For the tubes themselves, i am considering using the EHX 12AX7 ECC83 and EHX 6L6GC, mainly because they are still being manufactured and are easily available for me. Do anyone have experience with these, and how have they worked for you?

Also, I am aware of the safety concerns about working on something like an amp. But any advice or forewarning about anything people thinks is important would be greatly appreciated. Like i said, this is my first time working on something like this, and i do not have any ego in relation to listening to what people have to say. All help and thoughts will be really great.

[tremolo3]

I've never biased an amp myself (never understood very well what I really had to do tbh) but have modded/fixed some by swapping caps and resistors.

First and most important rule is discharge the filter caps, but you must have read this dozens of times by now.

[crochambeau]

I just peeked at a published schematic for the Ibanez TSA30, it's a trace, so I'm certainly not vouching for accuracy: https://gravinatubeamps.com/2014/08/02/ ... schematic/

If it is accurate, there's a trim pot you can twist to adjust bias supply. Regarding multimeter, it's only critical you use something rated at least Cat II (to say, at least 600 volts) for work on tube amps - avoid the $5-10 harbour freight stuff. I use one of these:

https://www.amazon.com/Klein-Tools-MM10 ... _indust_16
https://www.amazon.com/dp/B005FSSKJA/re ... 1_ST1_dp_3

The bias probe will probably come with instructions, but if not, each type of tube has a safe operating range of milliamps per tube, ****the operating range is affected by the plate voltage**** so, I'm not going to say something like "42 mA" because it will vary from amp to amp. This page will lend you some insight: http://www.tedweber.com/webervst/tubes1/calcbias.htm

Essentially: what sounds best to you within the safe window of operation is perfect.

Have fun!

[ibarakishi]

tremolo3 , Thanks for the safety advice and yes i had read about this a lot. I was curious also if the caps can be drained from simply not turning on the amp for a few days (with it being plugged into the outlet so that it is connected to ground?). I know that obviously it is safer to drain them the normal way, but out of curiosity will it naturally do this on its own somehow (or is there a way to let it do this natural)?

crocsambeau , Thank you SO much for the information and links. This is so helpful and extremely useful. I will read through everything you have sent. It is so difficult to find people to share information with about this stuff over here, so your guidance and insight is something i am thankful for in more ways than i can say in words. I am really excited

[crochambeau]

My pleasure, tube circuits are rewarding.

I know that obviously it is safer to drain them the normal way, but out of curiosity will it naturally do this on its own somehow (or is there a way to let it do this natural)?

Here's a quick write up I did ten years ago or so that touches on discharging caps: http://experimentalistsanonymous.com/orchard/page4.htm

It's part of this series, though much of the stuff in here is not directly applicable, and there are far more in depth resources out there: http://experimentalistsanonymous.com/orchard/

[ibarakishi]

crochambeau , Thank you for sharing your articles too! I will be interested to look around that site more as well. I looked at the first links you sent me for the multimeters, and think that i will probably try the uni-trend multimeter since i do not have a large budget to start with. When i have more money, i will then try to invest in something nicer with more options. For changing tubes and doing the biasing, is only using one multimeter (to plug in the bias probe) going to be okay and doable (the unit-trend)? Or will i need two multimeters to monitor multiple readings at once? I ask this because when i was reading about the 'plate voltage' and also watching some videos on the subject, it seems like many people use multiple meters to compare the different readings while figuring out these figures and while adjusting it to there liking. I have not read a lot yet, but am confused about how to figure out the plate voltage itself to use the charts that you sent me in the other link for the calculating the bias. I don't want to waste your time if you don't want to explain these things to me, so if you have a reference i could read to explain about this subject instead i would greatly appreciate it, but if you don't mind i would love hearing your explanation of it if you have time. And from what i understand, this is different (or how to find it is different) for each amplifier, correct?

I am sorry if any of my questions are obvious, i am thankful for your patience. I apologise in advance. This is very new for me, but i am excited to learn anything that i can about this subject and build my experience slowly

[crochambeau]

Use one meter - don't divide your attention. The B+ plate voltage is not going to vary much under load. I always direct measure it - CLAMP the common/black lead to the chassis, put one hand in your pocket or behind your back, turn the amp on, and carefully probe *predetermined* points (I go for tube pins and PSU capacitor points) in the circuit to read voltages, write them down if needed with your probing hand, turn the power off, and then remove your other hand from pocket/behind back/whatever. Under no circumstances should you steady the amp with one hand and probe with the other.

You're not after decimal points, just general ranges +/- 10% is usually fine, much beyond that (if you have published voltages to reference) and you might want to start sleuthing a little on what may be wrong.

Honestly, I'm quicker to grab my Uni-trend because it's easier to operate it one handed and hangs on a convenient hook via the clamp. I'm sure there are other comparable meters out there, those are just the ones I currently have and use.

[ibarakishi]

crochambeau , thanks again for the tips and information. I will go ahead and order what i need this month to start working on it. It will most likely get here in a month or two (shipping is a mess here). If i have any more questions, i will be sure to ask for your advice again in the future. Thank you so much for your help, and i am very excited to see your new pedal that you are releasing when it is finished too Your work is always exciting for me and i hope to purchase one of your pedals in the future as well