All things LA2a related

[Bluzzi]

I just bought some A-24 transformers and should be getting in a week or 2. (I was going for Sowter but managed to get UTC ones). Got my meters too and its getting exciting! A-10 and T4Bs next and then I'll be almost there.

Is continuety test good enough to test transformers? I'd just like to have an idea as it will be months before I gather all my parts and start wiring.

Thanks.

Jim

 

[CJ]

Yes.

 

[Bluzzi]

Thanks CJ! Continuety I can handle...whew!

Here's another question in my mind.

I bought 4 A-24s! I am building 2 LA2A so maybe I have all my audio transformers already. Do I have to mod anything in the LA2A circuit if I use an A-24 reversed as imput?

I'll be trying to get A-10s or Sowter but maybe I can get going sooner instead of waiting to get the other trannies.

Jim

 

[CJ]

A-24 reversed would be perfect for the LA2.Better than the A-10.

Less step up.

1:5 as opposed to 1:10.

No shields required at line level, especially with the humbucking structure of the UTC products. (two coils on one core, just like a guitar pick-up.

I wonder if Seth Lover stole his humbucker pickup design from UTC?

 

[Bluzzi]

Better! That is good. So I will go ahead and keep my eyes open for A-10 (only because I would like to hear the difference). But I will build the 2 LA2As with A-24s to start.

Thanks again for sharing your knowledge CJ.

Jim

 

[CJ]

No problem. Let me know how the A-24 as input sounds.
You should have better high end which will help, as the high end gets squashed durring compression.

:guinness:

 

[Bluzzi]

I will CJ - If you are willing to wait a few months! I still have many parts to get....and I'm buying way too many meters etc...can't help it...must stop...

 

[EmoRiot]

jim,

congrats on those a-24s! I saw them and considered getting them just to have around in case I build another LA2a, or four. :wink:

I've noticed that the bulk discount on ebay is strong. Each A-24 would have sold for just over 100 bucks each. But listing all four together comes up cheaper. Go figure.

What meters have you gone with?

 

[Bluzzi]

[quote author="EmoRiot"]jim,

congrats on those a-24s! I saw them and considered getting them just to have around in case I build another LA2a, or four. :wink:

I've noticed that the bulk discount on ebay is strong. Each A-24 would have sold for just over 100 bucks each. But listing all four together comes up cheaper. Go figure.

What meters have you gone with?[/quote]

Thanks. I was giving up on getting any and I feel I paid too much but I just want to get going on getting the main and rarest parts such as trannies and T4B (a T4B just sold for $200.00 on eBay! You can buy them new for $88.00!). So now I have 4 and as CJ says they can be used as input as well so I am not that desperate to get A-10 or Sowter.

The meters I got are Weston. Big black ones with 2 bulbs in them. They are cool and I prefer to Sifam.

I also got 4 other Westons but more modern look but also gigantic scale!

The Daven pots are neat and seem to still work (tried only with a VOM so maybe they are noisy).

I am building 2. One for me and one for my friend that has a recording studio and ......a MACHINE SHOP ! Ha! Amazing luck.

If they turn out great (just being cautious) I hope to make 2 more as I would like a pair.

I hope they turn out half as good as everyone else here. For me DIY is not to save money but to have the pride of having built something (even if its not my design) as well as learn a little along the way. I think there is something inside all DIYers that is a little of the mini scientist (mini for me not for the rest of you). We love to discover and chalenge ourselves.
In the end as I told my friend I will pay less for my LA2A in dollars but in time it will be 3 times over. I don't mind. I am finishing my studio for the same crazy reason. D. I. Y its crazy but its passionate.

(I don't know where that came from but there I said it and I'm sticking to my story).

Jim

 

[JerryPbury]

I'm shelving my first LA2A until I have completed my 2nd one.

I have checked every component and every connection (3rd time) and can find nothing different from the schematic. I layed it out according to the bloo instructions / Cayacosta layout and the only variance that I could come up with was at the R12 & R14 connections. Bloo instructions are flipped and Cayocosta layout is correct but labels are flipped. I also used a 10K/2W for R34 (22K is not consistant with schematic when using a 4.7K @ R28). I still have B+ (~330vdc) @ A19,20,21 & B20. I am at a total loss as to what is the cause. C7B? I don't know. I checked everything as suggested and it was all in line with what it should be (excepting the voltages) It passes signal and the gain stage works. Voltages at the T4B and neon are correct.

Thanks,

Jerry

 

[EmoRiot]

[quote author="JerryPbury"]Bloo instructions are flipped and Cayocosta layout is correct but labels are flipped.[/quote]

Could Jerry or someone else expand on what this means precisely. I'm about to start my first Bloo and I'm not sure if this is an instruction error I could correct preemptively.

thanks!

 

[Scenaria]

so if its passing audio.. and t4 looks good is it working or whats the symptoms of it not working?


realize that most of the voltages are approximate.... they will and can vary quite a bit depending on resitors etc.. I know on mine im using carbon comps that are 5% tolerance...

 

[Scenaria]

[quote author="EmoRiot"][quote author="JerryPbury"]Bloo instructions are flipped and Cayocosta layout is correct but labels are flipped.[/quote]

Could Jerry or someone else expand on what this means precisely. I'm about to start my first Bloo and I'm not sure if this is an instruction error I could correct preemptively.

thanks![/quote]

what he is referring to is the versions of the schematic...

 

[chriss]

Hi there,

I'd like to know where to best place a bypass-relais in the LA2A-circuit. Best would be inbetween the in- and out-transformers, so the chain is still transformer-coupled but you can compare before-after. But then: I guess the voltage at C5 is rather high. Can a normal relais handle this?
Any ideas upon this? I haven't found this discussed anywhere on the forum, so I try here.

thanks

Chris

 

[JerryPbury]

[quote author="JerryPbury"]This is what I have.

R29 4.7K / 2 Watt
R34 10k / 2 Watt
R36 470 ohm

It's just the voltages that are connecting to V4 @ pin 2, 5 & 6 (and affected connections).

Actual:---------Should be:
B21 370v------360v___+10v
A21 330v------275v___+55v
A20 328v------131v___+197v!
A19 323v------105v___+218v!
A16 47v--------7v_____+40v[/quote]

I tried it with an SM57->pre->La2a->amp-> 4" speaker. Sounded pretty much the same as when LA2A was bypassed. I couldn't reall tell if the gain reduction was working. I was just looking to see if it would pass signal and if it had gain. I haven't attempted to set it up yet (other than zero the VU) as I was concerned with the +200 volts @ A19 & A20! I am familiar with tube circuits using carbon comps (I have built 6 tube amps) and service all (10) of my tube amps. None of them have exhibited that much variance. The +55v doesn't concern me as my trannie is putting out +50v over.

I will be out of town this weekend but will attempt to set it up when I return.

Thanks,

Jerry

 

[Scenaria]

did you see deflection on your meter in GR mode? put a scope across the output to see if you can see the level reduce in GR mode...

 

[JerryPbury]

[quote author="Scenaria"]did you see deflection on your meter in GR mode? put a scope across the output to see if you can see the level reduce in GR mode...[/quote]

No deflection, but I hadn't adjusted the zero yet and it was near the bottom of the scale. Had plenty of gain. I could drive the amp into distortion and feedback quite easily. I will put it on a scope when I return from NC.

Thanks,

Jerry

 

[Scenaria]

hmmm

make sure the front panel trim can set that meter to zero first... your right if its sitting way at the bottom its unlikely you would see any movement

 

[JerryPbury]

[quote author="Scenaria"]hmmm

make sure the front panel trim can set that meter to zero first... your right if its sitting way at the bottom its unlikely you would see any movement[/quote]

The VU would raise up from the left at start up in GR, just not much. It zeroed from the trim easily. I haven't tried it out since adjusting the zero other than to check voltages again. It sure takes a while for the Electrolytics to drain, you can see it in the neon and the VU after shutoff.

Jerry

 

[Scenaria]

hmmm....

mine dont take that long to drain (when the tubes are in) I would say under 10 seconds...


so when you power it up with GR selected where is the needle sitting? at zero or a lot lower?