6550 Solarus with 3-4OT

[Kevin Sparka]

Hello Sunn gurus, any issues running the smaller 3-4OT on a 6550 tube Solarus with the 3-6PT?

I know overall power would be down alongside less bass / attack but wondering if it is safe for the amp/OT?

Any experience or reason this would be a terrible idea?

Thanks!

[EdBass]

It should work with a pair of 6550's, but not as well as the bigger iron. I suppose that's subjective since I have no idea what you are hoping to accomplish, but as you say the big, clean low frequency response would be seriously diminished.
Was the factory OT destroyed, stolen or compromised somehow?

It would never occur to my to try it, so I can't definitively say it's 100% OK as far as damage. My rule of thumb with vintage amps is to stick to the original design specifications as much as possible; with a recognition of modifications for increased/different modern power grid advancements (grounded chassis, beefed up filter sections, etc.).

A Smaller OT would never get on my radar. Let us know what happens... 

[Kevin Sparka]

Hi Ed, thanks for the thoughts. The original OT needs replacement (tested low power and unbalanced) and I have access to a 3-4OT I would like to try out.

I only use the amp for guitar, and I have read some older amps (fender etc) used smaller OT's in certain models and the result was "saturation" so am curious how this would actually work out.

My concerns would be it would still be running the larger PT combined with the high plate voltage and 6550's and if that would would be too much for the 3-4OT in this specific design however.

[EdBass]

Interesting. In the peak years, one of the challenges for Sunns with guitar players were that they were too clean. Still to this day Sunns are often thought as "Bass amps", however as you can see by the catalog section here, Sunn produced many more guitar amps than dedicated bass amps.

As with many vintage amps Sunns are based (in this case cloned) from a HiFi circuit. The Hafler designed Dynacos were particularly good at staying clean loud, with very deep bass response. You pretty much need to dime them to get any real nasty out of them.

You may have found the answer to that "too clean for guitar" challenge!

[Isaac]

Those dedicated guitar amps make great bass amps. too!

Can you guys explain some of the terminology you're using? What is a 3-4OT? Output transformer, certainly, but 3-4? 3-6?

[Kevin Sparka]

Hi Issac;

The 3-4OT is the code stamped on the transformer and was the smaller one used on the EL34 amps (about 3 1/2 inches tall).

The 3-6OT was used on the 6550 amps and is about 4 3/4 inches tall.

Both have a matching PT with the same designation/size.

[loudthud]

In general, any claims of OT saturation are made by amateur technicians or non-technical types with no idea what the technical definition of saturation is, or how to measure it. In short, they don't know what they are talking about and are just guessing.

From the Dynaco transformer info I could find, it looks like the 60W and 40W transformers had the same primary impedance of 4300 Ohms. The difference in power between the MK III and MK IV Dynaco amps was due to the difference in B+ Voltage.

A 40W transformer in a 60W amp will still make about 60W with a slight decrease in bass response and small increase in distortion. Dynaco transformers are tough and can probably take the abuse, but a tube failure might still damage the OT. Other brands of transformers are unknown.

[EdBass]

Triode sells clone transformers for the original Dynaco iron.  A470-S is their part number for the 40 watt PT, which was Sunn part # 3-40T, and Triode part #A431-S is their 60 watt Sunn part # 3-60T.

The original Dynaco/Dynakit part numbers were without the -S. just A470 and A431. Triode's primary business is for Dynaco HiFi enthusiasts, we Sunn-o-philes are lucky to have the resource. All of the old Sunns, guitar or bass designated, share those nearly identical Dynaco power amp designs, extremely HiFi and as 'thud says very robust compared to other MI amps of their era.

Still revered in tube audiophile circles, and sometimes referred to as "A poor man's McIntosh".

I wish Triode offered 120 watt Dynaco iron though...   

[Isaac]

Thanks.

[Kevin Sparka]

Thanks for the info Ed & Loud. Sounds like the word "saturation" was misapplied and it was really just more distortion with some neutered frequencies.

Looking at that Triode site they are indeed both 4300 ohms primary with matching response specs, the only difference is the smaller one has max DC per side at 80 ma and the large one 120 ma per side. They also both reference 6550/KT88 tubes as well so seems either one could work.