DT-25 topologies 1, and 3 not working. Have bought HD500 to fix this nonsense?

[richardbrown2]

Hi..

My DT-25 head does not select topologies A1 and A3. (well the lights come on on both, but it outputs weedy and barely audible sound)    

It sounds to me like a relay problem? (any thoughts)  All the B. selected topologies work OK..

 

So, I just bought an HD500 on evilbay to try to fix the problem, as sending it abroad even within Europe to get fixed  is silly.

I shall get it in about a week, with the intention to either ignore the DT-25 front end, and use all the HD500 models (via AES/EBU digital/audio Link cable.)  and to also be able to store sensible volume settings. 

 

My power amp works fine driving my DT-25 1x12"cab, and also when connected separately to a Fender Bandmaster cab. (both 8 ohms) so I imagine that the valves are fine.

 

I have no volume at all on DT-25 topology A1, (unless everything fully cranked, and then it's barely audible) and none on topology A3 either.  (same problem, and virtually un-hearable)

 

Topologies 2 and 4 are OK, with top A4 being devastatingly loud, and top A2, a reasonably OK clean sound..

Any thoughts?  Relay/s  or not?

 

------------------

 

Another conundrum.. Shall I be able to use the HD500 either to bypass (or maybe kick start ) the DT preamp ??

( ie. the HD500 might send a midi? data chain down the Link cable to 'unfreeze '  the non-working topologies?)

Have tried DT-25 reset a few times.. No joy.

 

If all else fails, and the DT-25 is not repairable,  I'll just use my trusty Fender Bandmaster and Bandmaster cab, and stick the HD 500 into its front-end as FX with modeled  pre-amps..  and I'll use the DT25 1 x12" cab for something else.)  

 

Seems a bit of a waste of a very good-sounding small cab, and it's severely annoying, having paid for a DT-25 head, that looks quite good (apart from the badge) and sounded good, but has now failed. :-( 

 

many thanks

 

ritchie

Bulgaria

[psarkissian]

It might be time to replace the power tubes (valves). When was the last time that was done?

 

[richardbrown2]

On 9/18/2024 at 5:55 PM, psarkissian said:

It might be time to replace the power tubes (valves). When was the last time that was done?

 

Thanks for your help.

The power tubes only drive the power output stage..   The output stage is fine, as I said. The power amp 'in'  works fine with an external pre-amp as input. (ADA MP1)

The 12AX7  valve (tube) would more likely be the problem in my opinion, as it is only concerned with preamp voicing.

 

However I suspect a relay problem or a relay actuation problem.   

Has no-one else reported topologies a1 and a3 not working?   (or at vastly reduced volumes)  If so, I cannot find any such reports here online, in any post.

 

A full re-valving of the DT would seem to me to be overkill, and a potential waste of money unless I can be sure that a full set of tubes is the problem.

Replacing a full set of tubes, and still having a possible relay/relay actuation problem with the DT-25 (with its inherent difficulties of repair, and no schematics available)  would just be an ongoing nightmare with no eventual solution in sight.

 

Main question:   Will an HD500 be a workable solution, and allow me to hear HD500 patches (with an AES/EBU digital/audio Link lead into the DT-25 ) ? 

If so, I don't care that I will be missing topologies A1 & A3 on the DT-25.

 

 

regards

 

ritchie

BG

[psarkissian]

Relay? Possible, but rare. Unequal topology is usually old tube (valve) elements wearing and

pulling down voltage of signal path in the tube (valve) amp section.

 

Also, be aware that topologies are not amplitude normalized between them, and that amp Class

setting is also involved in how the gain loop topologies work.

 

Schematics are not available due to intellectual property considerations, and we cannot vouch

for the technical ability of others out there. Being high voltage tube amps, it is also a safety issue.

I've been dealing with vacuum tubes and CRT's for 50+ years,... I still get zapped every now and then.

It still hurts when that happens. So another reason we don't publish schematics.

 

HD500 thru the Line 6 Link,... yes. I haven't tried that lately. As I recall, what comes out of the HD500

comes out of the L6 Link as well, fed by the same source path.

 

[richardbrown2]

Thanks for the info.

I shall order a set of tubes at the week-end, and hope that my DT-25 works properly when I fit them.. Not easy to get someone to properly bias them in Bulgaria, but I shall persevere.

I should get my used Pod HD500 next week, and maybe  I can move forward.

The AES/EBU digital/audio XLR cable to arrive after that.

 

I just want a decent clean sound, and not hot distortion.   What should the tubes be biased at?

 

 

regards

 

ritchie

BG

[psarkissian]

Use the tubes (valves) specified and matched sets, as specified in the post on tubes.

 

Remember,... these are not all analog tube amps, so the digital and analog sides have to talk nice to each other.