Need help testing pin voltage

[DizRotus]

In response to my earlier "Squealing 7199s" thread mdeneen and NOS440 mentioned testing the pin voltages to diagnose the problem. That thread seems to have gone to its grave before mdeneen and NOS440 revisited it to see my follow-up question regarding testing pin voltages.

Being new to tube gear, I can only guess at how to test pin voltages. My assumption is described in the earlier thread. Could someone please describe how to test tube pin voltages using a digital multimeter?

[DizRotus]

mdeneen,

Thanks for confirming my assumption regarding the mechanics of testing pin voltages. I'll do it for the experience, even though it probably won't solve the squeal.

Your memory is good. It's an SCA 35. I replaced the 4-section filter cap with the board sold by John Sullivan on eBay and used the parts that he suggested. There are more details in the "Squealing Sovtek 7199's" thread that Craig just resurrected.

The problem existed before and after the "upgrades" that are described in the "Sqealing ..." thread, so I agree with Craig that the Sovteks are probably the culprits.

Do you know if it is possible to adjust the bias on the SCA 35? If so, how?

If you get a chance to check out the "Sqealing ..." thread, I'd appreciate any comments or suggestions about what I've done or what you'd recommend to be done to this humble amp.

Regards,

Neil

[DizRotus]

mdeneen,

I'm interested. I would greatly appreciate a schematic showing the suggested mods, when you get the time. While I could not design modified circuits, I can follow a schematic and solder--and arc weld and braze--so performing the necessary surgery on the SCA 35 would be no problem.

I'm especially interested in finding alternatives to the 7199's.

Have you seen this web site: http://home.netcarrier.com/~rstevens/sca-35.html ?

If so, what do you think of the elimination of the tone controls? Does the suggested procedure make sense, or is there another way to bypass or eliminate the tone controls?

Thanks for your suggestions,

Neil

[DizRotus]

Norton AntiVirus is slooooowly scanning a PDF file that is being emailed. If it does not arrrive satisfactorily, let me know and I could mail you a CD with the schematic.

The email also advises that I use the SCA 35 to listen to CDs and FM on 1982 Heresys.

Neil

[NOSValves]

MDeneen,

Wouldn't it be better to go with a 6U8A if your going to change the phase splitter rather than a 6BL8. Of coarse I really have no Idea about the Dynaco curcuit just asking.

Craig

[DizRotus]

I'm not looking for more power, Just improved sound and the pleasure of working on the thing.

You asked about what replaced the 4-section filter cap. The following parts (excluding the Ruby 50/50uf 500 volt Cap that sits next to the cap board) were installed on the fiberglass PCB sold by Sullivan.

3 22uf mini Electrolytic

2 47uf mini Electrolytic

1 100uf mini Electrolytic

1 50 Ohm 5watt resistor

1 100 Ohm 5watt resistor

1 2200 Ohm 1 watt resistor

1 Ruby 50/50uf 500 volt Cap

It seems to work fine. It's my perception that it sounds better, but the difference is subtle. My DMM could only test the 20uf section of the old cap, which measured 15uf, but after forty years they were due to be replaced.

What is you opinion of the above as a replacement for the 4-section cap? Do you have an alternative?

The attempt to email the PDF file of the schematic failed. If you did not get at least one email w/o the PDF, let me know.

As I type this I'm listening to the Ed Love Jazz program on WDET, the Public Radio station in Detroit. It sounds pretty good coming through that SCA 35 and out of the Heresys.

Neil

[DizRotus]

FWI, please recall that the old phenolic (?) PCBs have been replaced by fiberglass PCBs. There is no additional space, but they are not brittle from age.

It would be no problem to snail mail schematic in print or on a disc.