Preamp Tubes for 2-hole 1979 DR-103?

[therealjoeblow]

Can someone tell me what the 'correct' and 'acceptable' options for preamp tubes are? I have a 1979 2-hole (canadian import) DR-103.

I believe it's supposed to have 3x12AX7 (ECC83) and 1x12AT7 (ECC81), is that correct?

Can I use 4x12AX7 without any modifications, or is that going to cause problems?

Also, if someone electronically inclined could elaborate, what would be the difference (IE, why one ECC81)? I know very little about tube amplifiers, but I've had this amp since I was a teenager and only recently took it out of storage to start playing it again.

Many thanks
The REAL Joe

[OldSchoolDave]

I believe it's supposed to have 3x12AX7 (ECC83) and 1x12AT7 (ECC81), is that correct?

Can I use 4x12AX7 without any modifications, or is that going to cause problems?

Maybe, Yes and No.

Later (Hylight) Hiwatts did specify 4 x 12AX7/ECC83's in the preamp section. That may have been a reaction to people putting the 12AT7/ECC81 in the wrong slot. Either way, you will do no harm to your amp.

The Phase Inverter tube (V4) is the middle one of the group of three. Using an ECC81 will increase headroom / lower gain. It's a matter of taste, but I prefer an ECC81 (or, better yet, a Mullard CV4024) in that position.

Dave

[Bossco]

+1 for Mullard CV4024 in PI position. Thankfully, genuine NOS are still available at good prices.
A bit more for the M8162 with gold pins version, which are my favorite.
Valve porn anyone?

MullardValve_M8162-CV4024.jpg (33.85 KiB) Viewed 1560 times

[mhuss]

Valve porn anyone?

The ECC81 has a bit less gain, but not a huge difference, since the gain is largely determined by the circuit values. For what it's worth, the unusual Hiwatt PI was designed for an ECC81/12AT7, although an ECC83/12AX7 works fine.

--mark

[JR]

I have a '78 DR103 canadian import that has had the canadian mod removed by Mark H. I have 4 Mullard ECC83 in my preamp and 4 Siemens EL34 in the power section. I think that the Mullards are a key element in the Hiwatt tone, (and the Marshall tone for that matter).