A "New" '67 Solarus combo and a lot of questions.

[soundmasterg]

What concerns me is the correct way to wire the "FB" circuit. I may have it wrong so I've included some pictures of that as well.
As a description of them, and this may not be all correct so forgive me ahead of time, what I'm seeing is:
The EL-34 tube that the "FB" wiring is added to has the "390pF" cap series connected between the #4 pin (G2) and the not used #6 pin.
There is a yellow wire that then heads to the intersection of the 470 Ohm & 680 Ohm resistors. Another yellow wire then leaves that point and heads to the terminal strip where in meets a 1K 1/2 W resistor which is wired in series with another yellow wire (of course) which heads to the yellow 16 Ohm winding's connection to the jack. Wired, I belive, so that when a plug is inserted into the "Speaker" jack the 8 ohm tab is lifted and the 16 ohm winding's tab makes contact. (..oddly enough wired just like the Scepter's jack's wiring without the 750pF cap in parallel with the resistor.)

O.K. so, it seems to me that the schematic is "wrong" but, not being an expert on Sunn's implementation of UL circuit design, what exactly is supposed to be "right"?! I have to admit that I can't get my head to 100% sure about this. I have looked through the forum but still haven't come up with an answer.
Please forgive me if it's there somewhere and I missed it.

Hi Mark,

In most cases, a UL connection means that the output transformer winding has taps in the output transformer at around 43% that connect to the screens, and the plates are wired as usual. Sometimes (Sunn 2000S) you'll see resistors in between plates and transformer winding, and also between screens and transformer windings, but the amp is still wired as UL. UL gives a power level between the typical pentode arrangement and triode connection but it reduces distortion close to triode levels which was useful for hi-fi, and works well for bass. UL has its own negative feedback, so when an additional negative feedback loop is added back to the phase inverter or in this case the gain stage before the phase inverter, it can be too much negative feedback and can make the amp feel cold and hard and the transistion between clean and distorted can be somewhat abrupt. One of the DR. Z amps (Route 66) uses UL but no additional NFB loop and has a good reputation for its sound with guitar. The NFB loop in this amp is much like that in a Fender where the output transformer signal is tapped out and sent back to the gain stage before the phase inverter (the pentode section of the 7199). Adding NFB widens the overall frequency response of the amp and cleans up the distortion, and makes the power amp less sensitive so it can take a larger input signal without distortion.

And pin 8 (K1) is at +105 Vdc when it's spec'd at +80 Vdc. +20 Vdc over spec'd voltage on both; coincidence? "soundmasterg" says that "7199" tubes can be "all over the place" but I can't help but wonder.

The 7199 has a triode and a pentode in the bottle. The triode is used as the cathodyne phase inverter and the pentode section is used as a gain stage. Pentodes can give very high gains even if the voltages are varied within a wide range, and as I said, in the Sunns I have seen, the voltages on the pentode section of the 7199 vary a lot and I have never seen one all that close to what the schematic said, but the circuit works fine and gives good sound and drives the phase inverter just fine. Subbing in a different 7199 would change the voltages or not, but they still wouldn't match the schematic closely. I wouldn't worry about it that much if those voltages don't match the schematic closely. Run a signal into the input on the amp and check stage by stage to make sure you can see the signal get amplified by each stage and you will be able to see if that part of the circuit is working close to the way it should or not.

Again, my gratitude for the education. Generally I try to take issues one at a time but in regard to power measurements of tube guitar amps; my understanding is that they are "designed" to distort at some point. So at which point (amount of output power) are they generally supposed to start distorting? ( either a Sine or Square wave.) I understand that the two different waves are useful for measuring different aspects of an amps functioning and or functionality but obviously need to study further on the topic.

As I said earlier, the usual procedure to quote the power on a musical instrument amp was to check the output power into a resistive load with about 5% distortion. Using a scope to monitor the signal and see when distortion occurs visibly, you then back off a little on the level to get a clean sine wave and then measure the RMS AC voltage at the output, square that number, and divide by the impedance of the load. So this is measure when the amp is clean. At some point the amp distorts, and you can run the amp all the way up and measure the output there too, and the number will be a lot higher. Tube amps have a transition range between their clean output level and the full power level where they give increasing amounts of distortion with lots of 2nd and 3rd lower order harmonics that our ears happen to find peasant and that we interpret as getting louder because of how our ears hear. Amps are designed to distort late with as much clean headroom as possible, or distor early with lots of preamp distortion for a heavier sound. Sunns were designed to be loud and clean, but any tube amp will distort when pushed.

(...I think I'll go pick up a new 5AR4. Old tubes are great but...) I'll continue when I pick up the new rectifier.

The vintage GZ34's are usually much better quality than modern ones and will last a long time....decades sometimes. A weak tube though won't work as it should so having a known good one on hand is useful. TAD sells the best modern manufacture GZ34 these days according to our friend Stan in Russia. What you might consider is to get a Weber Copper Cap WZ34 or WZ68. They are a solid state replacement that emulates the voltage drop and sag of a tube rectifier. They plug right into the socket so are easy to use. You can find them at www.tedweber.com. They are helpful to have as a backup and aren't that expensive...around $20 I believe.

Greg

[aavatech1]

SM Greg,

Greg,

In most cases, a UL connection means...

Thank you sir! I get it, it's weird. I think knowing that this particular amp IS wired correctly has allowed me to see it differently for some reason. I've read about NFB before but things just didn't add up with the uncertainty that I had about this Sunn's wiring. I'll be looking at the implementation on other guitar amps (schematics) and the older Dynaco stuff as well for comparison.

Run a signal into the input on the amp and check stage by stage to make sure you can see the signal get amplified by each stage and you will be able to see if that part of the circuit is working close to the way it should or not.

This will to be my next step. Given that both rectifiers resulted in the same voltages basically, that I don't need to worry so much about the "7199", the speakers are wired in correct phase, the NFB circuit is good and all other voltages are pretty much spot on I believe that your recommendation would be prudent at this time.

..procedure to quote the power on a musical instrument amp

After looking at a signal through the amplification stages I will accomplish this as well and document my findings of all here.

The vintage GZ34's are usually much better quality than modern ones and will last a long time

Both of the rectifiers mentioned above have been tested and passed handily. Do you find it odd that the "B" & "C" voltages are almost spot on with the voltage off the rectifier and the "A" (plate grid supply) voltage only being low? I'm feeling the need to look into the relationship between the plate/grid voltages, the negative bias voltage and supply voltages. Or are we having a uniquely Sunn moment? (..feels need for a "Flashback" emoji!)

As I write this I muse to myself about the difference between reading about all this stuff and a hands on approach to it's implementations. And man is there a lot of info out there on the subject of valve amplifiers for both stereo and musical instrument alike. A lot of what you've mentioned here I've certainly read before but I find it a lot of info to remember let alone put into practice. But I guess the operative word here is practice! The more you do the more you remember the better you get at it. And I believe that that is one of the things that makes this forum so very valuable. There is a BIG difference between working on this stuff while being the beneficiary of such helpful and knowledgeable people and having only books for reference.

My thanks again to you Greg, and everyone else, this is exactly what I've been needing.
OK,..back to the bench. More to follow....

-Mark>

[g1]

Just to (hopefully) clarify a couple points:

At first I thought you could run the "combo" speakers with another "External" cabinet. No such luck.
It seems to be one or the other. Plug into the "Speaker" jack; you get 16 ohm tap. Plug another cab into the "External Speaker" jack it "lifts" the 16 ohm winding and gives you the 8 ohm tap. So Conrad says "take your pick" ...but you can't have your cake and eat it too!

If your external cab. is 16ohms, then you want the 8 ohm tap when you are using both jacks. So, single 16ohm cab in 'spkr', or single 8 ohm cab in 'ext.spkr'. Or two 16ohm cabs, one in each jack. Each of those scenarios will be properly matched.
(I'm calling the 16ohm internal setup a 'cab' here)
I hope that helps put a bit of 'icing on the cake'.

I'm curious as to why you believe the 330K resistor is a mistake on the schematic. It was there when I received the amp and I just replaced the drifted carbon comp that was there.

I believe he meant the 330K to pin6 of the 7199. There is also a 330K to pin2&9. You have both?

[aavatech1]

Re: g1

Just to (hopefully) clarify a couple points:
If your external cab. is 16ohms, then you want the 8 ohm tap when you are using both jacks. So, single 16ohm cab in 'spkr', or single 8 ohm cab in 'ext.spkr'. Or two 16ohm cabs, one in each jack. Each of those scenarios will be properly matched. (I'm calling the 16ohm internal setup a 'cab' here) I hope that helps put a bit of 'icing on the cake'.

Yup, I stand corrected! I didn't think about the impedance of the two 16 ohm loads in parallel on the 8 ohm winding.
[Homer says; " mmm, louder cake!"]

I believe he meant the 330K to pin6 of the 7199. There is also a 330K to pin2&9. You have both?

Got it. Somehow I missed, or forgot, that he mentioned that he believed that it was that particular resistor that was the/a mistake on the schematic. Remedying it presently. Thanks for clarifying that. A definite miss on my part.

Thanks again "g1", quite kind of you to point those two things out.

-Mark>

[soundmasterg]

Do you find it odd that the "B" & "C" voltages are almost spot on with the voltage off the rectifier and the "A" (plate grid supply) voltage only being low? I'm feeling the need to look into the relationship between the plate/grid voltages, the negative bias voltage and supply voltages. Or are we having a uniquely Sunn moment? (..feels need for a "Flashback" emoji!)

Hi Mark,

It does seem odd that the first point after the rectifier has such low voltages. That power transformer looks like someone painted the end bells, or maybe it is a replacement? If you look closely at the endbells, are there numbers stamped into them? Say 606xxx or something like that? Every manufacturer has EIA codes that identify their company, and I believe Schumacher was 606. Yep confirmed...see the link. >> http://www.triodeel.com/eiacode.htm

So if that power transformer was replaced then that might explain the lower voltages on the B+. The rest of the voltages down the line wouldn't necessarily be proportionally lower as the circuit and values used tends to result in similar voltage drops. I don't think your amp is an earlier equipped Dynaco amp, but it could be. The number on the end bells should match between the power transformer and output transformer. The Dynaco amps had lower voltages, but not that much lower. Regardless, if the amp is working correctly even with lower voltages, then it should put out at least 40 watts RMS. Those voltages put it near what a 59 Fender Bassman is and those are 40 watts RMS for sure.

Greg

[aavatech1]

Hi Mark,
It does seem odd that the first point after the rectifier has such low voltages. Every manufacturer has EIA codes that identify their company, http://www.triodeel.com/eiacode.html

Hi Greg, It's got a "Western Transformer" installed. I had originally intended to post pics of both transformers earlier in the thread in case the info became pertinent. You should be able to see the markings on the "Western" but the output transformer is stamped "Dynaco A470" on the end-bell". The Western says: "Code: 1273" - "Customer No. 480" - "28-2340"

So if that power transformer was replaced then that might explain the lower voltages on the B+. I don't think your amp is an earlier equipped Dynaco amp, but it could be.
Greg

Given your previous statement I'm kinda thinking it's one of the "Dyanco equipped" models. The writing on top says "9/5/67". Generally I'm used to seeing workers sigs underneath things but..

I'm about to start that signal tracing procedure you mentioned earlier. And also take voltages after having removed that "Phantom" 330K resistor that 'g1' remarked was a mistake on the "7199" schematic. I'll be back in a few with the results.
Thanks again Greg,

-Mark>

[loudthud]

Western Transformer was a supplier to Sunn. Their factory was in Portland on the West side of the Willamette just South of the Ross Island Bridge. Gold painted end bells were kind of a trademark.

a scope measured 16 VPP (16*16=256/2.83=90.45/8=11.3 W).

You divide p-p Voltage by 2.83 before you square it. The answer should be 3.99 Watts.

This is the 330K resistor I think is the mistake.

[nsubulysses]

LT, for a quick tangent as per the Western Transformers, was this a brand that was only available for a certain period of time, or was it coveted in some way compared to the Sunn amps that had black end belled transformers?

I ask because people have asked me if I know anything about why model Ts with gold transformer end bells are sometimes considered "special" and are worth more money. I told them I had never heard of that

[nsubulysses]

For instance, in this pic both Model Ts do not have gold endbells but the T on the left has Western transformers. The T on the right has some other brand. Do you know what they are ?

[loudthud]

I ask because people have asked me if I know anything about why model Ts with gold transformer end bells are sometimes considered "special" and are worth more money. I told them I had never heard of that

I've never heard that either. Back in the 70's it was hard to find off the shelf power transformers for 100W solid state amps. I wanted to find out how much it would cost for a custom wind and was referred to Western Transformer by a junior college teacher. It was more than I wanted to pay so it never went any further. What I ended up doing was taking the PT from an old TV, unwinding all the secondaries and winding a new secondary.

I never made the Sunn connection until later after I started collecting old amps. Maybe Soundmasterg can ask Conrad if he remembers anything special about Western Transformer.

[soundmasterg]

Maybe Soundmasterg can ask Conrad if he remembers anything special about Western Transformer.

I was planning on doing that this weekend as I had never heard about the Western Transformer/Sunn connection. I thought there was just Dynaco and Schumacher. I'll post here if I find anything out.

Greg

[aavatech1]

You divide p-p Voltage by 2.83 before you square it. The answer should be 3.99 Watts. This is the 330K resistor I think is the mistake.

Hey loudthud,
I removed the 330K resistor and the 7199 voltages dropped +10 Vdc at G2 and K1, the "excessively" high voltages I was getting previously. EL-34 plates rose ~+5 Vdc but the B+ is the same. Currently the 7199's G2 and K1 are still a bit high but per Greg's advice I'm not sweating it but feel a little better after it becoming that much closer to the schematic's values.

Also, thanks for the info on the math..excuse me a second, OUCH! O.K. I"m back.
3.99 W sounds like there's something seriously wrong. Considering all of the circuit voltages being so good I'm thinking that the problem may be with my measurement devices.. In particular the dummy load. It's an odd contraption that came with an organ repair company's stock I purchased a few years back. Anyway I've got another one on the way and it should be here tomorrow (Fri). I'll then do the measurements again and report. I had planned on getting a "proper" high wattage dummy load for some time and the time seemed right currently. (..probably should have a long time ago)
Thanks again loudthud,
-Mark>

[nsubulysses]

I was planning on doing that this weekend as I had never heard about the Western Transformer/Sunn connection. I thought there was just Dynaco and Schumacher. I'll post here if I find anything out.

Greg

very curious to hear if you get any info, but I bet it's probably just one of those things that vintage amp people tweak out about. it might not be better, but it might just sound better................to talk about.

You know how it goes with the old gear, "oh yeah I have one of those old sunn amps but I have one of those rarer ones with the gold top transformers." That's what I heard it referred to as, gold top, because they are laydown transformers in a Model T.

sorry to slightly derail the thread

[J M Fahey]

Sometimes a Manufacturer gets some parts from other than the "established" supplier.
Maybe he got a few free samples to try (or bought a few to test), or had to ship a batch and was missing a few transformers so had to get them somewhere else or ... or ... or ....
Nothing too special about it, but collectors sometimes attach undeserved importance to such details.

FWIW sometimes people runs out of some colour paint and uses what´s available on the shelf, "now", it has no special meaning.

[aavatech1]

..a mean RMS

You divide p-p Voltage by 2.83 before you square it. The answer should be 3.99 Watt.

loudthud:
The new dummy load arrived today and I decided to use the digital scope-meter instead of the Tektronix as it provides an RMS reading of AC signals. The results are displayed below. From the "Speaker" jack (16 ohm winding) I'm getting 16.30 VAC before clipping into an 8 ohm (200W) load. Then using the correct formula: (16.30^2=265.69) / 16 = 16.6 W (pic 1) Then at full volume max RMS voltage is (17.6^2=309.6) / 16 = 19.35 W (pic 2) Then from the "External" speaker jack (8 Ohm winding) 17.00 VAC (17.00^2 = 289) / 8 = 36.12 W Then at max volume: 19.2 VAC. (19.2^ = 368.64) / 8 = 46.08 W

That sounds more like it. Sound about right for the B+ and plate voltage? It's also looking like there's not a whole lot of ramp up into that area of breakup. Just like Greg was saying, (I'm paraphrasing) pretty much clean as a whistle up until the very end!

Question: I've read different things from different folks about the voltage used for injecting Sine and Square waves into an amp for testing but what would you all say? I still intend to measure the signal voltage gain at the differing stages. Considering guitar output voltages can be all over the place depending on pickup style, playing style, pre-amps etc, is there a baseline generally used? Would one consider this more of a troubleshooting protocol or could it be used for checking individual stage functioning? I'm thinking the answer is "Yes". ; )

-Mark>