Assemblage ST-40 with dead EL34

[ScramMan2]

I had an EL34 go last night. I saw it glowing, and just shut down the power.

I replaced the entire quad of EL34's with another known working quad.

I get no power to the unit at all. There are no fuses on the back. I'm thinking there may be an internal fuse. I have not pulled the bottom cover off to take a peek, nor have I pulled out the schematic to check that. I just pulled the unit out of my rack and put my PL5 back into action. Nice to have that as a "spare"!

Any ideas or experience with this amp? If I can't see anything obvious I'm going to take it to my tech on Friday. They just rebuilt some DCM TF's for me, and I told them I'd be back, but not this soon.

 

[AudioSoul]

Sorry, I dont have an answer for you. I just wanted to post because you dont see any Assymblege ST-40 amps mentioned very often. I just put mine back into service today. It is a great little amp. It sounds better than my Forte model 4 class A amp that I was using. I have less than ideal tubes in it, EH EL34 big bottles........:thmbsp:

 

[byoung334]

Check the rectifier tube

 

[ScramMan2]

Check the rectifier tube

Don't think it has one? Uses 4 - EL34, 2 - 12AU7, and 1 - 12AX7.

There is a fuse on the power supply circuit board. I have not pulled the bottom cover off to take a look. Will do that this afternoon.

 

[kvflyer]

Rectifier may be diodes (solid state). Also, could the coupling capacitor become leaky upsetting the bias on the output tube? I don't know the amplifier either. However, that would be my first guess...

 

[ScramMan2]

Rectifier may be diodes (solid state). Also, could the coupling capacitor become leaky upsetting the bias on the output tube? I don't know the amplifier either. However, that would be my first guess...

I'll look closely at the power supply when I open the unit up.

My guess is that when the tube went south it took something else along with it. I might be in over my head.

 

[DALEK S D L]

I'll look closely at the power supply when I open the unit up.

My guess is that when the tube went south it took something else along with it. I might be in over my head.

I think your right. Sadly when EL34's short they tend to take out resistors below the valve base and possibly elsewhere on the circuit board. I for one would recommend when you get it fixed replace the EL34's with 5881's( if your amp will work with 5881 valves); these are a military spec substitution for the EL34. They are more reliable and if they go they usually don't blow the crap out of anything. Sound better too IMHO.

I use new re-issue Tung-Sol 5881 valves and they are excellent. Hope you get your amp fixed soon


Regards Neil

 

[GordonW]

5881 is actually a version of the 6L6, not the EL34.

However, I think that they can be biased up, and will work, in the Assemblage/Anthem amps of that era.

If you did that, I'd think about stepping up to the 6L6GC rather than the 5881. Rated at higher voltage (like the EL34) and more watts of dissipation (can handle more abuse. Another good option is the KT77 or KT88... they can also usually be used as substitutes for the EL34...

As for the amp at hand- I THINK the Assemblage does have an internal fuse. Some of the Anthem products (also made by Parts Connexion/ Sonic Frontiers) did, from my recollection, at least...

Regards,
Gordon.

 

[DALEK S D L]

Thanks Gordon

When I think about it your right about the 5881 call it a senior moment. Yes I must get round to trying 6L6 tubes some time...they should work okay in my Audio Innovations series 1000 mk3's mono amplifiers, its auto biasing...no volt meters needed.

Roger gets 100 watts out of his Music Reference RM200 amplifier which use KT88's, nice amp well worth looking for S/H if you need lots of power. I have a MK1 but I haven't heard his new MK2 version, which may be better (knowing Roger it is better as he doesn't change things just for the sake of it).

Regards Neil

 

[WhiteSE]

Isnt the guy from PartsConnection, the fella from Sonic Frontiers/Assemblage?

 

[ScramMan2]

Isnt the guy from PartsConnection, the fella from Sonic Frontiers/Assemblage?

Yes, the two "Chris's" that founded Sonic Frontiers put out the Assemblage kits, and also own Parts Connection.

I sent an Anthem pre-amp to them for repair earlier this year. They did a great job on repair and turn-around. The shipping and brokerage fees into Canada makes it too costly.

 

[ScramMan2]

Rectifier may be diodes (solid state). Also, could the coupling capacitor become leaky upsetting the bias on the output tube? I don't know the amplifier either. However, that would be my first guess...

When I mentioned the sequence of events to my techs they said "coupling caps" right away. I have all the schematic and parts info, so they should be good to go.

This amp was built from a kit, so there is plenty of info there. I am the third owner. I don't think the other two listened as much as I do. The last owner said about 4-5 hours a week. I do that in one night.

 

[ScramMan2]

Can you guys educate me more on using other tubes as a substitution for the EL34?

If I use a 6L6GC what to I set the bias at? The EL34's use 40ma (bias was correct last time I checked, I am handy with a multimeter).

I have GL Gold Lion re-issue KT88's in my PL5, but I'd prefer not to mess with them (it has auto-bias).

 

[ScramMan2]

Update. The JJ EL34's did not fry. I had the same quad going on my PL5 last night. Bass does not sound the same though.

 

[ScramMan2]

I have the ST-40 back. It has some awesome deep fat bass sound with the Groove Tube EL34's. And the JJ's.

Got some new Tung Sol and EH on the inputs.

 

[ScramMan2]

I like the EL34 output sound over the KT88 (Genalex Gold branded under PL label.)

 

[ScramMan2]

5881 is actually a version of the 6L6, not the EL34.

However, I think that they can be biased up, and will work, in the Assemblage/Anthem amps of that era.

If you did that, I'd think about stepping up to the 6L6GC rather than the 5881. Rated at higher voltage (like the EL34) and more watts of dissipation (can handle more abuse. Another good option is the KT77 or KT88... they can also usually be used as substitutes for the EL34...

As for the amp at hand- I THINK the Assemblage does have an internal fuse. Some of the Anthem products (also made by Parts Connexion/ Sonic Frontiers) did, from my recollection, at least...

Regards,
Gordon.

There was an internal fuse that went. Right on the power supply.